Deconstructing: Nimblebit – Bit City

The latest release from Nimblebit features the Bitizens and this time they’ve used an idle/clicker/tapper crossed with a city builder in their new release of Bit City (iOS / Android). I’ve been a long time fan of the Nimblebit team, started by the brothers Dave and Ian Marsh back in 2007 but expanded to a number of other key staff. My personal favourite game of theirs was Tiny Tower, but I’ve also played and churned out from most of their newest releases. Pocket Frogs deserves a design mention as it still has one of the best collection/rarity mechanics of any game that I’ve played on mobile. Nimblebit specialises in creating a collecting or simulation experience around common everyday objects.

Bit City’s core mechanic is an endless economic growth game and the aim of the game is to progress through the 8 increasingly sprawling cities to generate the most income per second.

Clickers in General

The clicker or idle genre is one of the more recent but extremely popular free to play mechanics that we’ve seen on mobile. There are some great reasons why the mechanic itself has been present in many large successes such as Adventure Capitalist, Tap Titans or Egg Inc. At it’s core, the loop for a clicker is very simplistic. You’re trying to improve your rate of earning, in order to buy items to increase your rate of earning.


The simplicity of the core loop is both a blessing and a hindrance. The fact that everything you do in the game contributes to making you better at what you do (earning currency) feels very rewarding.

Every action is a positive action.

The hindrance comes when you eventually find the core interaction (tapping as fast as you can) repetitive and boring. In some clicker games, this can happen very fast. So, as a game designer, you eventually shift the player’s motivation from tapping to something that will last much longer. The clicker game genre eventually shifts into a strategy of choosing what to upgrade next. In Tap Titans 2 a player is strategically shifted from upgrading characters to gathering gear, pets or items. All of these have random drops and XP to give much more strategic depth. Upgrading anything feels good, but timing and choice matter.

No one can be expected to be active in a game forever which is where the idle aspect of most clickers come in. While you’re away your game is playing itself, constantly growing your earnings. That way when you come back, a stockpile of cash for you to quickly spend and improve to feel powerful. This happens every time you come back, whether it’s 10 minutes or 10 hours, the size of the stack changes but the feeling of reward stays the same.

The genre itself appeals to a certain type of gamer. Those obsessed with finding the most efficient and time-effective way to improve their progress (in the form of earning rate). Sometimes referred to as min/maxers finding 1-2% efficiency in upgrade choice is rewarding as you are progressing. Yet even the casual player feels good, you’re constantly making progress but at a lower rate. If you’re more interested in story and context then you will often not feel as excited about idle games. It is a game for fans of stats and numbers.

Bit City – Context provides content

Idle games began on the web with titles such as Cookie Clicker or Cow Clicker released around 2012-2014. These games were incredibly simple. They drew huge numbers of returning users every day as the objective of “having the highest number” is so clear and powerful for players.


In more recent times games such as Adventure Capitalist, Tap Titans, Farm Away, Make it Rain have re-skinned the mechanic and given a context to the clicking. Context helps with design decisions as you immediately add more depth. Depth provides you with content and that content can better mask the simple stat progression. Player’s decide their goal is to “build the greatest city” rather than to “get the highest number” and this creates a better sales pitch if and when they tell their friends about your game. Context helps you design and it helps you sell, use it to your advantage and don’t neglect it by slapping it on at the end of development.

Bit City provides much more context to the clicking experience by using a city and it’s buildings to provide more visual substance and reference to the core loop. The City Context is a good one, used in multiple genres it’s easy to reference, has great depth and is applicable to people from all countries. Bit City uses this to great effect, but adding Building Zones, Cars, Planes, City Hall and Windmills each contributing to your currency earning.

Clicking = Building

Core Interaction of Bit City

The core mechanic of tapping furiously on the screen has been removed in favour of the idea of building. One must purchase and classify lots so that buildings of specific type are built. Buildings then fill each lot and the large Build button upgrades and refreshes the building on each lot for a small increase in coins per second earning power. The upgrading of buildings is endless and rather than getting stuck in a content farm black hole, the buildings are upgraded at random. Every upgrade levels up the block and each subsequent upgrade adds 1 second to the total time required to build the next block, leading in the later game to upgrades take minutes. Choice of which block to upgrade is removed from the player through randomisation and the player is taught very quickly that every upgrade is beneficial.

This is a very strong mechanic for a number of reasons:

  • Thematically it makes sense. Your city changes with time and you can position blocks in certain areas to make your city look beautiful
    • You may also lock in place any buildings you particularly like allowing the creatives build beautiful masterpieces of a modern renaissance!
  • Choice paralysis is removed because you don’t need to choose what to upgrade and all upgrades are beneficial.
  • Build timers slow down sessions giving people incentive to leave.

As a pacing mechanic, it continues to engage at all stages of the game. This is often one area that other clickers loose me on as in the mid-late game, I simply stop clicking…

City Planning

Simplicity and clarity are always key design decisions for mobile game developers. People spend a few minutes at a time with your game and so everything needs to be clear and make sense in an instant. The choices available to a player in Bit City always relate to upgrades. The most profitable upgrade you can do is buying a new building for your city as each building provides a larger base earning rate. A really nice design feature is the idea of city zoning. There are 3 zones, Residential, Industrial and Commercial. Within this feature is a lot of shallow depth, that is there are a very large number of options and possibilities but as a player, the way they affect the game is incredibly minor. They do not affect the core in any way, they simply provide a route to micro-optimisation, reinforcing the fun of clickers.zoning-bit-city

Each building zone is balanced by providing a 10% bonus or 10% deficit depending on the overall % of zones, this promotes people to build in an ordered manner. At certain times you may want to opt for larger investments in certain zones because both the Mission system and the City Bonus system provide bonus’ specifically based on type of building built. This is a good use of shallow depth again. Most people would not obsess over the minutiae of which building to build, but to really get the most optimisation at each minute of gameplay it might be valuable to invest in specific zones at specific times.

Missions with increasing reward

Another clever design decision is to reward ever increasing premium currency (Bux) by completing missions. Missions usually revolve around building, improving or owning some upgrade or building. mission-system-bit-city

There is only one mission available at a time and they seem to be structured to appear in a specific order. Rather than having a small payout with lots of quick missions to teach people the mechanics, Nimblebit have used missions to give players a longer term goal. The cleverest of these is the ownership of 2 of the same building types i.e (2 Baseball Fields).

Mission systems are one of the classic mid-term progression systems. They provide a steadying hand and a focus for players when options of what to do open up. The best mission systems are usually curated or at least missions are grouped and then provided based on XP level.

The Premium Currency (Bux) are gifted in 10 bux increasing increments. This is risky, as it becomes a significant source of Bux in the mid game. I think the progression is a nice touch but the size of the progression is too high, it would have worked just as well say, 10,12,14 etc. At mission 13 I’m on 130 Bux which is equivalent to $0.13. Each mission can take an hour or more, but sometimes you might complete 2 or 3 in a few minutes. Although it might not seem a lot it lessens the requirement to spend. In the mid-game, it’s most profitable to focus on and perform the mission at hand. Balancing the rewards and spend of the premium currency is definitely one area that Bit City could improve on.

Progress, Profits, Prestige

Modern clickers increase the gameplay depth over time in a number of ways. These usually either increase the speed of clicks (Faster), the value of a click (More) or automating the clicking process entirely (auto). Each of these upgrades has a clear and tangible benefit, they help you gain more currency quicker, give your players a choice: do you invest in yourself being active in the game, or invest in the time you’re inactive?

Each city comes with a set number of plots. 4 for a level 1 city, 8 for a level 2 city etc. As you build more buildings you start to max out your plots. As soon as you have maxed your plots a new city unlocks and you sacrifice all of your upgrades and buildings to start again. This creates a clear goal for gamers and eases gamers into the game via small cities. As you progress the cost of each new building starts to become prohibitively expensive which encourages you to want to sacrifice everything in order to prestige to obtain Keys which will speed up everything in your game for the entirety of your play time.


System Diagram of Nimblebit – Bit City


What’s very pleasing compared to other clicker games is that the speed of progress is managed by a multiple limiting factors. Limits by multiple sources feel elegant rather than a strong single limiting factor. First, the coins themselves slow progress as you can’t build enough buildings, then the plots limit progress on one city as you max them out and finally the cities themselves become prohibitively expensive unless the global tap multiplier is improved by prestiging.

Prestige is very important as it adds ebbs and flows to an otherwise linear progression. Every time you do prestige you suddenly feel incredibly powerful as you race through early content, this is important as rather than having to create more complexity players are re-engaging with the game and reinforcing the simple systems of the game and progressing incredibly quickly. Bit City has created “mini- prestige’s” every time you upgrade to a new city once you have maxed out your plots. With every reset there is a sense of loss but also a sense of growth, getting your players used to this feeling helps them engage with the main Prestige mode.


In the mid to late game idle games, prestige currencies become the main goal in Bit City these are Keys. It’s very important to get the balance and the feel of Keys right. In Bit City, Keys feel underpowered as the quantity of keys provided when you prestige is too small. A user wants to feel progress at close to double the previous rate when they sacrifice all of their upgrades. Doubling up whilst keeping a logarithmic increase in the power curve of costs equates to half the time spent getting back to where you previously were. One you reach your old position the logarithmic power curve kicks back in and really winds back a player’s progress to a snail’s pace forcing them to prestige again.

A player chooses when to jump to the next prestige level and effectively picking at the right time can jump you onto a much more powerful curve. Great game design in this area wouldn’t use perfect logarithmic numbers but would add some randomness and inconsistencies to make it a guessing game for the player to find out if they are maxed out at an inefficient area of the curve.


Time taken to reach a city in bit city.  Prestige levels and number of hours are representative and not factually correct.



It’s not mentioned in mobile how important the user interface is for a game. Especially in these management style games with large amounts of details, getting information across clearly and concisely is a challenge on a small screen. Nimblebit do a number of great reinforcements.

  1. bit-city-star-towerYour key measure of progress is represented as a large central number of coins per second present on every screen.
  2. The build button (the button you click the most) is larger, more centralised and stands out from the rest.
  3. The subtle nuances of the game such as plot size, or building type are reiterated to you when you need the information, such as the quest system (large service)
  4. Before you make a large choice there is always a confirmation screen ensuring you are happy with your decision.


This attention to detail of the user’s journey removes frustration from the game. It allows you to choose where to focus your attention on to complete one or two of the tasks at a time and speed up your progress. A nice font and simple language make it enjoyable to read.

Monetising – Keep a tight grip

I’ve spent $10 so far in Bit City. For that, I got 10,000 bux. Bux are the only premium currency and are used to speedup progress, buy city upgrades that persist through prestige mode as well as unlocking certain famous buildings that provide enhanced bonus’. I feel that this was the point where the game design suffered.

  1. Bux are not a rare currency within the game. You can get 10s if not 100s of bux by completing missions or taping on vehicles that randomly drop bux, as a free player you can often buy a few persistent upgrades. When purchasing these upgrades there is no delight, magic or drama and as a player, all you see is your bux amount slowly draining. Purchasing the unlock of rare buildings was also much the same with a simple UI transition from locked to unlocked within the building card screen.
  2. No early conversion purchase. The Builder in Clash of Clans or World Multipliers in Adventure Capitalist, which immediately are the best bang for your bux! *pun intended…
  3. Gauging the value of upgrades is difficult. For instance, Market Gains for 1000+ bux increases your Bank Savings rate by 1%. This feels minor but would have a huge effect on the earning power itself. Rather than so clearly affecting such a powerful rate, investing in 20% cheaper bank upgrades would have had a similar effect to the player but would be immediately noticeable.
  4. No sense of mystery or delight when spending bux at any point. All bux are spent with a simple click and a UI change.
  5. No random drops. With it’s huge array of buildings creating a clear building rarity scale and then having a random drop element would make every bux much more exciting to spend. Random rewards have spikes of joy, rather than a focussed

I suspect the number of people purchasing bux will be low, simply because the number given out in-game is very high and people can immediately get a sense of what it would be like to have 1000s of them by spending a few hundred that they got for free. Games with great conversion rates keep the pressure on players to want to spend by constantly showing the value of having premium currency to progress. Bit City treats bux too loosely and as such the pressure to get my wallet out is low.

Video Ads – Double Time

I suspect that the game’s primary monetization route would be video ads. There is currently only one method to engage with a video ad through the opt-in button called “Double Time”. The value proposition here is strong, for a short period of time, double everything. Directly doubling the speed of progression is the best feeling for a player because it directly contributes to that core loop. Things that feel great in-game are strongest when they contribute to your progression directly. Clickers, by their very nature, are all about progress and so the reward is clear and easy to feel.

Unlocks happen more regularly I can build more buildings and progress shows a real gain. The upgrade itself is time limited to 10 minutes but with bux can be upgraded to 15 or more minutes. This again is a clever gamble as by getting people to potentially invest in an IAP they then encourage more video views, which if you remember is a key KPI for increasing monetization from video ads.

The major issue here is that there are not more ways to engage with video to improve those views per DAU that lead to more revenue. The 10-minute bonus is strong, but what about a 4h increase in the Bank Savings rate? Watch a video ad to upgrade a building directly would provide so many more places that a user could click the Watch button, increasing its adoption. The classic Double Up bonus for all returning players could be run once every 24 hours in order to highly incentivize at least one valuable video view per day. There is huge scope for expanding video ads integration.

Conclusion – Great Core, Monetization need Tightening

Bit City is a great example of expanding clicker mechanics into new genres. City Building and Clickers make a great match because of the depth in buildings and environment that are available to the team. Nimblebit have done a really good job of pacing the game across multiple cities causing you to have clear evolutions in your progress as well as allowing you to prestige at any time, making it your own decision. The type of upgrades and the thematic choice of upgrades fit nicely, all contributing to a busy and bustling city experience. The UI and UX of the game itself is also neat, simple and clear making playing the game an enjoyable experience.

The game’s biggest weakness will be its monetization. It’s very loose usage of Bux as a reward currency and the fact that players can only interact with video once per session without enough cues from the UI. The value of that video view is high so it should see good usage, but providing your most engaged and active players with more ways to watch would see many more views per DAU.

The games a great addition for the Bitizens and well worth a play!

Is Supercell’s Smash Land too Simple?

Supercell’s most recent soft launch is called “Smash Land”. It’s been in soft launch phase in Canada and Australia since March 31st 2015 (About 2 months from this post). There is no doubt that Supercell’s soft launches are huge news for the mobile free to play industry. Supercell is notoriously picky about what games that make it to soft launch. Each new game goes through rigorous internal feedback, and only the best games survive. The games that hit soft launch are games that Supercell genuinely believes have a shot at the Top Grossing charts.

Smash Land is based on “Monster Strike”, a massive mobile free to play game in Japan. In December 2014 it took over Puzzles and Dragons’ top spot in the Japanese charts. Similar to how Supercell started Clash of Clans with looking at Backyard Monsters, Supercell now looks to simplify the design of Monster Strike so that it could work in the Western markets. But in Supercell’s simplification of a game that performs so well in Japan, has the game stayed intact?

Has what remains kept what is required to be a successful game?

Smash Land’s Core Battle

Supercell decided to keep core battle game the same as Monster Strike. The core battle mechanic is a Physics-based RPG battle. Almost like a game of pool, the game is mostly about predicting how balls on a flat surface will bump and move to create a preferred outcome. In Smash Land, the game is about lining up one of your characters so that it bounces between walls, enemy characters and your own characters as many times as possible. The player then collects up to 10 different heroes, each with their own special ability. For an overview of the mechanic, watch this video:

Overall the core battle feels smoother, cleaner and is much easier to understand than Monster Strike. Each character feels unique because of their special abilities which feels great.

The gameplay is very strong for a mobile F2P game. Its easy to pick up and understand for any player. The feeling of skill is strong — I can predict a few bumps and feel smart about setting up strong combos. On top of this, because of the nature of physics, Luck comes into play. Like Peggle, physics is usually pretty easy to predict after the first shot, but after the first few collisions it becomes almost impossible to predict the outcome. As a result each move can result in some “Post-Action Luck” which is critical for casual games.  Players feel smart and each shot is unpredictable.

Overall they’ve taken the best bits of Monster Strike and applied it to a more focused experience. It’s a great battle system that is easy to get addicted to.


Outside of the battle, players can also engage in upgrading their heroes stats. This is really where Smash Land departs from Monster Strike.

Monster Strike contains far more variety of stats for each character:


Just comparing these two screens you can see the dramatic comparison between the games. Its much easier to understand Smash Land compared to Monster Strike.

However, at what cost is this simplicity? In Smash Land the major differences between the characters are special abilities and their health to damage ratio. In Monster Strike, the team you bring into battle requires far more strategy as you progress in the game.

You need a balance of elemental types on top of ensuring you’ve got strong special abilities that are complementary. My guess is that while Supercell’s game clearly scores points for understandability, it will seriously limit the long term replayability of the game compared to Monster Strike. Players just won’t have nearly as much to strategize about in the long run.

Smash Land also departs from Monster Strike in how upgrades are handled.


Heroes are upgraded with gold and time. So the player collects gold from playing matches or collecting them from treasure hunts, and turns this gold into upgrades to their heroes. The cost of each upgrade escalates very quickly. As a result, the game really starts to require many, many battles before you can afford a single upgrade.

Smash Land’s system is far simpler than Monster Strike. Monster Strike takes cues from Japanese Gatcha games like Puzzles and Dragons. To upgrade your heroes you must collect hundreds of characters and consume them to give experience points to your heroes. For a great overview of Gacha, read here.

Leaving the Gatcha system out for Smash Land is a big risk, what remains is a far too simple economy that quickly becomes a grind.

Monster Strike’s system with consuming & collecting monsters has a massive advantage in the long run compared to Smash Land. Instead of just 10 heroes, Monster Strike has almost 1000 collectable monsters in the game (source). With this massive set of monsters, they have created a system where players have much more excitement for the long run.

As I’ve spoken about before, to alleviate the feeling of grinding it’s all about creating random spikes of progression. Similar to games like Diablo you need to find ways to add luck to your progression. Ensure that each battle can result in a lucky outcome which could dramatically increase their pace of progression. In Diablo this could be finding a legendary weapon on the ground which makes it a breeze to beat the enemies following.


In Monster Strike, instead of powerful rare swords, players can randomly get awarded rare monsters from the gatcha system. The player now feels lucky, like the game gave them something for free that should have cost them real money or a lot of time. Because the player got this rare monster, they can rush through previously hard levels and feel great.

Overall the rate of progression may be slow, but because there are these moments where progression randomly spikes, players are far more likely to engage for a long time.

This variable progression is missing in Smash Land. To progress, you must upgrade your  heroes in a linear path. Each victory gives you a calculated amount of rewards. The cost of upgrading a hero grows each time.

Overall, with only 10 heroes and very limiting upgrades, the metagame is just too simple. I have the same heroes as everyone else, the same upgrades as everyone else, so there is no moment where I feel like I’ve got a really unique set of heroes that are more amazing than my opponents. Without this unique feeling, it is hard to get attached to my characters or get attached in the long run.

Desirable Stats

Smash Land removed plenty from Monster Strike when they simplified the heroes/monster collection structure. But regardless of how many collectable characters you have in your game, if you want players to engage in an upgrade system you need to ensure that those upgrades are desirable.

IMG_0108 (1)

In Smash Land my drive to upgrade is very weak. The battle overall feels very Skill & Luck driven (as I described above). The outcome of battles has more to do with getting repeated bounces over how much each player’s heroes had levelled up. In many cases I won with far fewer levels than my opponent, or I lost at the hands of an opponent that had far fewer hero levels than me. This translates in less player demand for upgrading their heroes. Instead of having a strong desire to have the strongest possible team, players will blame victories on their skill or luck and will more likely be content with their team as is. This is a difficult balance to get right in any game. For more on Stats vs Luck vs Skill, read on here.

But for this game, where its whole monetization plan is dependant on players upgrading their characters, Stats must take more precedence in the outcome of a battle.

If the player has a decreased desire to upgrade their heroes, then this will break how the game monetizes. Hero upgrades are at the core of how this game makes money. Players grind for coins (or spend money), on top of have long timers (8 hours or more) to upgrade their characters. After spending money in the game, speeding up the upgrades all of my characters substantially, I really didn’t feel any more powerful in the game. I lost subsequent multiplayer battles, and was now facing an even higher upgrade cost for my heroes. In the end spending money in the game really just didn’t feel worthwhile.

Overall Thoughts

If this wasn’t launched by Supercell, this game would never have gone under so much scrutiny. The game on its own is polished, fun to play, and ticks all the boxes for being a successful free to play game:

  • Strong Pacing of content
  • Multiplayer gameplay to provide long tail retention
  • Guilds to bring players together without requiring Facebook
  • A simple game mechanic that’s easy to pick up and play, hard to master

But when you put them all together in this game, the metagame is too simple:

  • There is not enough variety or strategy in choosing heroes
  • Upgrading quickly becomes tedious and a long grind
  • There is not enough desire to upgrade your team to compete at the highest level

So how will this do on the market?

So far it seems Supercell is keeping this game in a quiet soft launch. Comparing this soft launch to Boom Beach, by 2 months Boom Beach was higher in both the download charts and grossing charts within Canada (source:AppAnnie). That points to Supercell keeping the marketing costs & number of new users down for the time being while they improve the game. Supercell is very rigorous with their soft launch games. Just last year they released “Spooky Pop” which failed to hit their targets. As a result they decided to cancel the game.

Can Supercell turn this game around during the soft launch? I think it will be difficult. They cut so much away from what made Monster Strike work, its hard to see if small feature additions will be able to rebuild what’s necessary. It will only happen if they completely rebuild their Hero progression systems.

I think Smash Land should be an example for all future mobile game designers. Simplicity can open up to wider markets, but the focus on Free to Play must be on long term retention, not the widest audience. Game designers must strive to create enough longterm depth in their metagames, or else they will fail.

Addendum (02.07.2015) :

According to VentureBeat Supercell has decided to shut down Smash Land.

The team clearly worked very hard on the game and created a wonderful product. This just reiterates the fact that creating hit games on the mobile AppStore is extremely difficult, even for the best developers.

I look forward to what Supercell constructs in the future!


Hearthstone: A Game Changer for Mobile F2P?

Blizzard’s Hearthstone has defined collectable card games (CCGs) on mobile over the past year, and with the recent launch of the versions for smart phones on both iOS and Android the mobile revenues have rocketed roughly sevenfold.

Hearthstone is an interesting game to look at, because it breaks so many of the conventions of mobile F2P:

  • It has no energy system
  • It sells only permanent items
  • It is highly skill based
  • It is mainly synchronous PvP

As such it appeals to a lot of self designated “gamers” that find other mobile games somehow below them. This run down of the game will take apart the main features and discuss how they create and great game, and whether there are larger implications for the mobile F2P industry.

Core Loop

The core loop in Hearthstone is incredibly simple:


There are two main play modes: Ranked and Arena.

Ranked can be considered the basic game mode, where players play against each other synchronously to climb a monthly ladder. Players use decks that they have constructed from their permanent card collections. It is free to play, and players earn coins for winning matches and completing quests that appear daily.

Arena can be considered a secondary play mode, but is hugely important to and complements Ranked play. Here players also play synchronously with each other, but they must pay an entry fee – either coins or real money. Players make a deck as they enter the arena, choosing one of three cards at a time until they have a full deck. The rewards depend on a player’s performance, but can be generous compared to the entry cost.

The balance of the two modes is important, because it provides both payers and non payers, as well as players of different skills something to do. Earlier on, players may find Ranked play easier as they learn to put together decks that rely on specific combos. Later on they may find Arena more fun as there is the challenge of putting together a deck on the fly, and all players have the same chance of getting legendary cards.



Quests act as the pacing system in Hearthstone, but it is so well framed that many players don’t see it for is. Rather than restricting the number of matches that players can play in a certain time, quests limit the amount of coins that a player can earn. Players get one new quest each day, and are limited to having three in total at any one time. Players can earn small amounts of coins for winning matches in Ranked play (10 coins every 3 wins), but this is small both compared to the time it would take to play these matches (perhaps 30 minutes or more on average), as well as the coins earned from quests (40-100 per quest).

As players earn most of their coins from quests, and not from playing matches, Hearthstone has no need to limit the amount of times a player can play. Players can (and do) sink hours into climbing the rankings without breaking the economy, as after the first few games their in game earnings are virtually nil. This is such a simple yet effective feature I am amazed that more F2P games have not copied it – energy systems are by far the most hated, yet standard F2P systems.

Single currency, single resource

I count coins as the single currency in Hearthstone and dust as the single resource. Hearthstone does not have a soft currency for everyone and a hard currency for payers. It follows therefore that it does not have items that can only be bought for hard currency. Purchasable things in the game can either be bought for either coins or real money. Dust is reserved exclusively for crafting specific cards.

The fact that as a non payer you can get anything in the game, and you can earn coins at a reasonable rate, helps create an environment that seems fair and inviting for both payers and non payers alike. Whilst the temptation to drop real money on a bunch of packs is constant, it never feels like someone has beaten you just because they’ve spent money on the game.

Permanent purchases


The nature of card rarity in Hearthstone also supports the feeling of fairness. Cards have one of four rarities: common, rare, epic and legendary. However, in contrast to many of the other mobile CCGs, cards cannot be upgraded or fused. This means that buying cards always results in a permanent addition to your collection, either directly or through the crafting system.

As with all CCGs there needs to be some method of dealing with duplicate cards, to maintain the randomness of pack opening. Hearthstone only allows players to have two of each card (one of legendaries) in their deck. Duplicates beyond this can be disenchanted for Hearthstone’s main resource: dust, which in turn can be used to craft any card in Hearthstone. The conversion rate is obviously not great – cards give only 25% of their cost to craft when they are disenchanted, and making progressively rarer cards gets ever more expensive. You need to disenchant 320 common cards to craft a single legendary. But the system does mean that even if players only get duplicates through randomly opening packs they can work towards specific cards that they want to create particular decks.

The fact that purchases result in permanent items that cannot be taken away from the player makes them all the more attractive. Players know that if they get a legendary card they will always have it, and its power will stay constant. Players can still spend huge amounts of money on the game, as there are so many cards to collect and the chance of getting a legendary is so low. Various Reddit posts put the cost of a Legendary at around $12-24, so with 67 legendary cards currently players could easily spend over $1,000 getting all of those alone. The cost of the epics and rare cards would be on top of that, and players can pay 4x for cards with a gold back – a purely cosmetic change.

Buying Experience

The permanence of purchases together with the overall polish in the game creates an incredibly positive buying experience. You would expect nothing less from Blizzard of course, but the pack opening sequence is spectacular, especially when compared to the drab experience in many mobile F2P games to skip a timer or add more resources. Buying something feels great, a detail that is all too often overlooked.

Skilled play vs. Pay to Win


Most mobile F2P games steer clear of including too much skill. Skill makes games more difficult to balance, as players will have a varied experience of the same content. Furthermore, with highly skilled games it is difficult to give players a continuous sense of progression, as their skill level will typically plateau after an initial learning period. As most mobile F2P games are selling progress, they need to maintain the sense of progression that grind based games give, as ensure that players have broadly the same experience by leveling the playing field with luck.

In contrast, Hearthstone has a high degree of skill – the game has an impressive number of tournaments and events, and Blizzard host a World Championship at BlizzCon that had a prize pool of $250k last year. Youtube and Twitch are awash with Hearthstone matches and the top players are starting to make their fame and fortune from the game. This is clearly a far cry from games like Clash of Clans or Game of War, where success largely depends on the amount of time (and money) players can grind into the game.

That said, in Ranked play, working your way up gets more difficult the higher you go not only because you meet more skilled opponents. Any player will tell you that you need to both have the right cards to put together in a deck to create the right combos, as well as the ability to change your deck as you go. This flexibility is vital as the meta game changes as you move through the ranks. At a given time, rush decks might be unstoppable at ranks 20-15, but easy prey above rank 10.

Always having the right epic and legendary cards to finish off your deck becomes essential, but you rarely need very many of them to create a good deck. The pressure to spend is in having the necessary breadth of cards, rather than a deck construct solely of very rare cards. This creates a dynamic where players do need to spend to play at the highest levels, just as League of Legend players need to practice with all the different Heroes rather than just the ones that are freely available that week. At the same time each individual card is balanced for its mana cost and players who have spent a lot of money to acquire a lot of different cards might be beaten by a player who has spent very little, but happens to have the right cards for that particular battle. Players must spend to progress in general, but matches don’t feel pay to win.

Synchronous PvP

Hearthstone is one of the only successful mobile games to centre on its synchronous PvP experience. Vainglory and others have tried to take this challenge on, but no one else has succeeded except another game backed by a massive desktop IP: World of Tanks Blitz. Hearthstone was in beta on PC 9 months before coming to iPad, and had half a million downloads before it even hit the App Store. This period was essential to give them the critical mass needed to match players with each other at an appropriate level. Without it players would either be facing long wait times every match they played, or getting matched against players of very different skill – either case is a potentially game breaking experience.

Blizzard’s ability to drum up this level of interest in a new game is a testament to their expertise at launching new synchronous PvP games, but absolutely not a reference that other developers can hope to emulate. Without Blizzard’s existing World of Warcraft IP, installed fanbase, community management efforts and PR, the game would have faced a much harder prospect of building the community necessary for critical mass. I do not believe that we will see a synchronous PvP based game successful on mobile without a PC version any time soon.

Wrap Up

The success of Hearthstone, combined with how different it is from many other mobile F2P games makes you expect it would have a huge impact on the prevailed design trends in the industry. The pacing system in particular seems superior to the energy systems that are still prevalent in many games. However, the fact that Hearthstone was launched PC first on the back of the huge World of Warcraft brand has allowed a number of other differences that the vast majority of mobile F2P developers cannot hope to emulate.

Deconstructing King of Thieves

Let’s take a deep dive into ZeptoLab’s latest game: “King of Thieves”. Launched in February 2015, this game has piqued my interest. While not on the top spot yet, the game’s bold design deserves a look.

In my opinion, this is a game that deserves to be successful. It feels unique and has all the elements that make up a top grossing game. ZeptoLab has taken what works in simulation and strategy games, and applies this to a totally new genre and a completely new target audience.

This approach is what I feel more new game designs should do to be successful on the AppStore.

The Pitch

The pitch for King of Thieves is “Super Meat Boy” combined with “Clash of Clans”.

Untitled drawing

The core gameplay is a one-button platformer. Your Thief (the little cute black shadow) automatically runs left or right. You can tap to trigger a jump in the current direction. You can also jump off walls to reverse the players direction. ZeptoLab has managed to give classic platformers a mobile makeover. With one-touch controls it feels native on mobile. With simple rules, it feels expressive and gives players plenty of options. The gameplay is simple and is very transparent about what you did wrong each time you die. This creates very addictive core gameplay. 


The object of each level is to reach a treasure chest. Go from “point a” to “point b” by avoiding traps. Hitting a trap will reset your progress right to the beginning. This punishment gives the game the “Super Meat Boy feel”. Reasons for losing are always clear to the player, and there is very little friction to restarting. The player jumps back into the action as soon as they are killed, making it extremely addictive to just keep trying to beat a level.

The meta (the progression systems outside of the core platformer gameplay) is a re-hash of Clash of Clans. They’ve managed to modify the standard Clash of Clans formula into something that works very well with the core platformer gameplay. Just like Clash of Clans, King of Thieves asks the players to manage two layers of gameplay: attacking and defence. On attack, the player plays platformer style levels to steal gold and gems (more on this later). On defense, the player must design a base that defends against other players’ attacks. Players sessions are focused on stealing as much loot from players around the world to upgrade their own abilities.

The Session Loop

To deconstruct, I’d like to focus on session design. To do this, we need to break down the game into its daily action loop: the repetitive actions the player takes to progress in the game. Let’s evaluate each step in regards to how it impacts the way the sessions feel.

Looking back at the post on Flexible Sessions, the key principle of designing sessions is about creating a diminishing curve of value for sessions per day and for session length. Just to reiterate: The first rule is that the first session of the day should feel more impactful than the 2nd, 3rd, or 4th time the player returns. By the 5th+ session, this should give minimal value to the player. The second rule is that session length should also have a diminishing curve of value. Eventually a player should naturally feel that returning at a later point in the day would be more beneficial. These two rules make up strong session design.

So how does King of Thieves execute this?


Step 1: Collect Base Rewards

Each day the player begins their session with collecting the rewards from their dungeon:

  • Collect gold from their stash. (Optional Short Timer)
    This is a bucket-filling mechanic. Allowing players to collect from the stash as many times as they wish throughout the day.
  • Collect gold from successful defences. (Short Timer)
    Making sure players feel good about their defences, players collect gold for every failed attempt by other players in their dungeon. While not a lot of gold, this certainly feels good when you’ve come back after a long absence
  • Collect generated gems (Long Timer)
    Gems generate on the map on a longer cycle (multiple hours). 

You can see here that these three reward cycles each have varied timer length, which allows for strong session design. Short timers to value coming back more per day, but longer timers to reward daily play. Using rewards of varying length, the player has a clear diminishing value for returning multiple times throughout the day.

Step 2: Loot Dungeons with Keys

After the player has collected all their rewards, they want to maximize their cash for their current session. There is always the threat that other players in the world will steal any resources they have when they leave the game.

Players can choose between the PvP (left) or the PvE (right)
Players can choose between the PvP (left) or the PvE (right)

 To do this, players loot other player’s dungeons (PvP levels) or designer-created levels in a map (PvE levels). Player-created levels hold high value gems. Whereas the PvE levels have higher gold rewards (sometimes), unlock new gem generating mines and new dungeons which the player can move to. This system works because both PvE and PvP benefit the player in different ways.

 King of Thieves innovates with their pacing mechanics. Instead of using energy or lives like in most games, they use “Keys”. Keys refill like in most games with time. The key difference is that the amount of energy (or keys) the player needs to spend to enter a level is randomized.

Players can choose a lock. Each attempt costs a key. Only one of them gains entry. Randomized Energy.
Players can choose a lock. Each attempt costs a key. Only one of them gains entry. Randomized Energy.

The player chooses locks on a screen with their keys. If they get the right key, they enter the level. If they choose the wrong one, they must spend another key. The game supplies the player with more than the usual amount of energy (10+). However, some levels can use 1 key to enter, others up to 15 keys to enter. Why would ZeptoLab design a system like this?

This system doesn’t please all player types. I’m convinced ZeptoLab benefits more from this system than the player experience. Not an easy choice I’m sure as a designer, but these sacrifices are sometimes necessary in a free to play game.

 From the onset, this system feels arbitrary, just like an energy system. The player’s ability to loot is capped by some tacked on economy. Compared to Clash of Clans, Clash’s pacing mechanics make sense: you will eventually run out of troops to loot opponents. King of Thieves just says you run out of “keys”. Could this be fixed if the player had to “craft” keys in their base? Could this be fixed if the player had to build clones of their shadow player to start looting? Maybe. Overall I’m not a fan of the system, but I understand the benefits for ZeptoLab.

 Because the system is randomized, players can try for one more level even if the player only has 1 or 2 more keys left. If they get lucky, this feels great. They get to play the level with little cost. If they fail, they are presented with this screen:


This screen is a high conversion screen for their video ads. Want to keep trying? Watch a video ad. Video ad revenue is becoming more and more interesting in the mobile free to play space, and I completely understand why ZeptoLab wanted to create a pinch point for this type of system. Players then binge watch some videos to get in that “just one more play” feeling.

On top of converting players with video ads, this type of randomized energy system also creates a nice way to balance harder and harder levels. Players can upgrade their key storage limit to be able to reach higher and higher levels. The higher the level, the more locks that the player must attempt. Also, this can create an interesting session per day value curve. ZeptoLab can use metrics like sessions per day and session length in their decision about how lucky the player is. This may be dubious, but this type of “invisible hand” to guide the session design can be very powerful.

In the end, I’m unsure if this system of randomized keys was the best choice for King of Thieves. The system is a unique design and I’m excited to see what the market thinks of it. Just based on the conversion to video ads, I think this could be something to try for other genres.

Step 3: Upgrade Your Base (or Else!) 

After the player has looted as many dungeons as they could in that session, they may use their found coins to upgrade their dungeon and resource generation. Any coins left over will most likely be stolen, so players attempt to spend every coin they looted. This promotes going for one more looting session, or extending the session to purchase more gold.


Step 4: Fuse Gems

 The key to the meta and progression of the game is fusing of gems. Players collect gems from mines on the world map and by looting other players in the world. The player then takes the gems collected and fuses them in their base.

 Fusing usually takes many hours (3+ hours for a usual gem). During this time the gems in this fusing ritual are open for stealing by other players. This is the most anxiety-inducing timer in the game. A gem will be stolen unless they keep the game open or have amazing defences. I spent about two hours on a weekend keeping the game open while watching movies because I was too afraid to close the app and lose my gems.

So why would players opt-in to this nerve wrecking timer?


Increasing gem value is the goal of King of Thieves. The total value of your gems is how you rank in the game. Players are looking to retain only the highest quality gems (which is shown by a number). However, there are only limited slots the player can have to hold onto gems. So players quickly run out of slots and are forced to fuse gems together to make more slots for higher level gems.

This was a very, very smart design choice by ZeptoLab. This creates a natural cap for progression and creates a lot of very interesting choices for the player. It also creates an obvious high conversion item for monetization: the extra slots for gems. Similar to the builder in Clash of Clans, ZeptoLab has created a high conversion item out of these extra slots. I’m convinced that if they brought this to the forefront and made it cheaper for first time players, this could be a strong conversion item.

Step 5: Optimize Defences

After they’ve completed this loop: collect, attack, upgrade, fuse… what’s left?

 Just like in Clash of Clans, players can extend their sessions by optimizing their dungeons defence layout and adjust the positions of traps. This comes with one caveat: the player must be able to beat their own level twice… in a row.


This definitely creates a session extension. I’ve spent well over a half an hour trying to create the optimal dungeon design. All this time was not incentivized by the game, but I wanted the best layout possible. This is exactly what you want to create in your session design. A session extender that players can take as little or as much time with as they wish. The value diminishes over time.

What they did right: Social Pressure Mechanics

ZeptoLab shows an excellent example of how to add effective social mechanics to a game. Asking players for help to retrieve lost gems creates social pressure. I feel good about helping my friends, I enjoy when my friends help me out when I’m less active. I rely on my friends to help me optimize my fusing timers. The value of having active friends is apparent.


 The league system creates a nice PvP environment with a clear reason to collect gems. Instead of feeling like I’m levelling up just based on some arbitrary number the designer has created for me (ex. collect 5000 gem value in 5 days), I’m competing against a living breathing opponent. I have to be engaged to compete, and the number is always growing so I never feel safe about my position. Sometimes I wish there were ways to specifically steal from other players on the leaderboard you were competing in. This would really drive up the competition.

King of Thieves also uses the same idea of clans in Clash of Clans. King of Thieves wants you to join a Guild. While the system is clearly in its infancy, it shows a commitment by ZeptoLab to the future of the game. Guilds are what will really drive the long term retention, and including it in the global launch was important. The mechanics at this point are still too early, but in the coming months I expect that ZeptoLab will build from this base and make very competitive play between Guilds stealing gems from each other. I hope they find a way that Guild members can work together on a dungeon or a raid. It would also be interesting to incentivize Guilds to put their most valuable gems in a vulnerable position. This will really drive competitive gameplay between the Guilds and give a collective goal.

What they could improve: Hardcore Skill

 In the translation of the Clash of Clans metagame to Super Meat Boy style mechanics, something fundamental was lost. Because platformer gameplay is inherently so skill-based, the translation still feels like a massive amount of skill is required to win.

 Clash of Clans (as discussed before) although it requires some mix of stats and skill, the main determinate to win each fight is Stats. If you have an amazing army, you are going to win. If you have spent a ton of time (or money), you will be able to dominate against an opponent lower than you. As you defeat more of these easier players, you will be matched higher and higher in the leaderboards. This will demand more skill, but mostly more stats. This system allows players to “hover” around matchmade opponents that challenge their skill level, but still require high stats. Even if I’m terrible at selecting where my troops go, I’m still progressing, and I may be lower on the leaderboard compared to other players at my stat-level, but I still am progressing.


King of Thieves is never flexible over the amount of skill it requires from players. As you progress in the game, it keeps demanding more and more skill from its player base. As a result, the game feels very hardcore. The players that reach the end game are a smaller and smaller niche of highly skilled players. Why does this happen?

As the game progresses, players slowly get harder and harder obstacles they can place in their dungeon. In order to set up a dungeon that is difficult, the player has to beat it themselves. As a result of this system, unless a player is highly skilled, their dungeon, regardless of the defences, will remain at the same low level of skill-difficulty. There is no way for a player to increase their defence without actually being far better at the platforming game.

There are some stats that affect the game: the damage of the obstacles, your shadow’s equipment and armour, the amount of keys you have, etc. But these stats clearly take less of a precedence over the skill. In my opinion, there are some levels that you just need high skill. So as you progress in the game, no matter how much time or money you’ve put into the game, you will reach levels that it doesn’t have an impact if you don’t have the skill. There is no “hovering” in the matchmaking that allows players to feel progress regardless of skill. Players with low skill will feel it: they are punished by losing levels very often.

This is most likely an artifact of trying to combine a high-skill genre (Super Meat Boy) with Clash of Clans. While this pushes away players that are expecting a lower skill level, I think it also engages the highly skilled players even more. The tradeoff between a highly engaged niche target audience and a flexible broad audience appeal is incredibly difficult to get right.

The Results:

On launch, the app was featured by Apple. This drove hundreds of thousands of downloads, but has yet to crack the Top 100 US Grossing. Can it get there? This will be a extremely tough. After a featuring, the only way to drive the necessary volume to reach the Top Grossing Chart is to purchase installs. This is extremely costly.

However, the game supports very strong early day retention and with more work can improve their long term retention. With continual improvements this game has a chance to reach a stable position in the Top 250 Grossing.

Personally, I’m cheering for ZeptoLab. This design is refreshing. I had the feeling that the mobile free to play space is even more risk-averse than the console/pc space. This feels like a step in the right direction. This is a game ZeptoLab should be proud to have worked on. I hope other game developers can look at this example on how to innovate in new genres