Clash Royale’s Economical Design

Video Games

Clash Royale

Clash Royale has been my go-to phone game lately. I didn’t pay it much attention when it launched early last year; I just assumed it was Supercell’s latest entry in the “shouting man icon” mobile game genre. But it kept popping it when I was searching for new deckbuilding games to play, so I decided to give it a shot.

Belying its wacky cartoonish aesthetic, Clash Royale is actually a very elegantly designed real-time strategy game (with a tolerable free-to-play metagame). Players select 8 cards (troops, spells & buildings) for their deck, then spend “elixir” to deploy them on their side of a two-lane arena. Their units will push towards the opponent’s side of the map, with the aim of toppling their three towers. The entire battlefield fits on a vertical phone screen, and matches only last 3-4 minutes.

Players select where to summon their units, but they fight autonomously once deployed1. This simple touchscreen interface is approachable for mobile players, but there is deep skill and strategy in the timing and placement of deployment. In essence, Clash Royale refines mechanics from the notoriously complex RTS, MOBA and deckbuilding genres into a very elegant and accessible hybrid game.

While there’s a lot to praise about Clash Royale’s design, I’d like to expand on a small detail that caught my eye. It’s an ingenious design decision that allows the developers to efficiently reuse their existing content. It also opens up strategic options for the player without sacrificing simplicity.

Skeleton cards from Clash Royale

Skeletons are the weakest units in Clash Royale. They die in one hit and their melee attacks deal negligible damage. The base version of the card spawns 4 skeletons and is one of the only 1-elixir cards in the game. It’s mostly used as a quick distraction, tanking damage from a stronger unit while your towers whittle it down. Its low cost also makes it good for an emergency defense. Because it’s a common card that fits well into beginner decks, players will very quickly get a sense of a skeleton’s relative strength and strategic uses.

A different card, Skeleton Army, deploys 14 skeletons for the cost of 3 elixir. This has an obvious benefit in elixir efficiency (2 extra skeletons for the cost), but it also provides a distinct strategic utility. A horde of weak units can easily overwhelm stronger units that have high hitpoints and move slowly. Skeleton Army is a hard counter to Giants & Hog Riders, two of the strongest pushing units in the game. However, a concentrated swarm is more susceptible to AOE spells, giving the opponent to the option to trade effectively using Zap or Arrows.

Concocting two cards from a single unit is pretty good, but Clash Royale goes even further. The Witch is a slow-moving AOE-damage unit that summons 3 skeletons in front of her every few seconds. The Tombstone is a low-cost defensive building that periodically spawns a skeleton, and spawns 4 additional skeletons on death. Finally, The Graveyard is a legendary spell that gradually summons a swarm of skeletons in a large radius. It can be deployed anywhere in the arena, even directly on top of your opponent’s towers. Each of these five cards gets to reuse the skeleton code and assets while serving distinctly different strategic purposes.

A similar design pattern is used for goblins, which are a slightly-stronger base unit. They come in two basic flavours: Goblins (melee) and Spear Goblins (ranged) both cost 2 elixir for 3 units, while the Goblin Gang summons 6 goblins (3 of each) for 3 elixir. Goblin Hut is a building that periodically spawns spear goblins, and Goblin Barrel delivers 3 melee goblins anywhere on the map.

Goblin cards from Clash Royale

From a production point of view, there are many benefits to this type of content reuse. Supercell have stated that they keep their game downloads under 100 MB, which is the maximum size that iOS will allow to be downloaded without wifi. Having multiple cards use the same unit models, textures, and sounds is a huge benefit to Clash Royale‘s memory footprint. I suspect that the minor unit variations (such as the melee and ranged goblins) likely have some shared assets. This decision undoubtedly helps with development scheduling as well, as they can create more content in the same amount of time.

Furthermore, this approach also has benefits for game design. Once players understand a unit’s strengths and weaknesses, they won’t be confused if that unit pops up in a different context. For instance, I remember the first match where my opponent played The Witch. I had to take some time to observe and understand her behaviour, but the skeletons she summoned were a known quantity. I felt confident about reacting to them.

Having fewer individual unit types simplifies game balance and tuning. If The Graveyard spell were to hypothetically summon it’s own bespoke unit called the zombie, then the design team would have to reconsider the zombie’s strength relative to the skeleton every time either unit was adjusted. Keeping the units consistent allows Supercell to focus instead on what makes each card unique. For instance, they’ve nerfed Skeleton Army twice this year by simply reducing its skeleton count by one.

Designers often fret about reusing assets, fearing that players might burn out on repetition. Clash Royale’s economical design demonstrates how clever tweaks to existing content can afford distinct strategies for the player. NPCs are more than their base stats; variations in quantity, economy, and deployment are cost-effective ways of reinterpreting existing units.

1 Purely incidentally, the game actually has a lot in common with Pax Britannica.

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Montreal International Game Summit 2016

Montreal, Video Games

Uncharted 4 AI Debug

On November 15th, I’ll be speaking about combat design and AI in Uncharted 4 at the Montreal International Game Summit. My talk explores how we navigated the extremes of combat design philosophy (tightly authored vs fully systems-driven) throughout Uncharted 4‘s development, and how we found our best results with a hybrid approach.

Ahead of my talk, I did a short interview with Brendan Sinclair at GamesIndustry. We discussed a number of topics related to AI design, including why our early attempt at a simple point-to-point search behaviour failed:

“In another instance, they used some pathfinding AI from The Last of Us to get enemies from point A to point B. Gallant said it was soon clear that the AI worked especially well in The Last of Us because the game’s tight, complex environments ensured that the enemies would traverse environments in mostly human ways, using aisles and doorways, walking around desks and other obstacles in the layout. But in Uncharted 4‘s larger, more open layouts, moving from point A to point B usually meant travelling in a perfectly straight line, which wasn’t terribly interesting.”

“The solution was to run paths throughout the layout that AI would move along, trails that would have them reasonably making their way throughout the level, perhaps clearing out corners or other places the player could be hiding on the way to their destination.”

Attending MIGS this year is also a nice homecoming for me. Not only was I born and raised in Montreal, I was actually a student volunteer at MIGS way back in 2009. It’s a real honour to be able to come back as a speaker seven years later.

You can catch my talk at 3:45 PM in room 519A on Tuesday November 15th. If you’re attending MIGS, I hope you’ll swing by to say hello!

Disclosure: As a speaker, MIGS is covering my flight & accommodation during the conference.

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A Taxonomy of Randomness in Hearthstone

Video Games

Hearthstone: Whispers of the Old Gods

“RNG gets your emotions really high and really low. It makes you really feel. Sometimes when I play a game I’m just going through the motions and I’m not getting those highs and lows, but in Hearthstone I get them all the time. It makes me want to come back and play more.”

Mike Donais, Hearthstone senior designer

Randomness is a perpetual topic of conversation among Hearthstone players. It’s generally accepted that a game with random elements can be highly skillful and competitive. However, each new expansion revives fears that Blizzard may have tipped the balance too strongly towards luck at the expense of high-level play. The evolution of the game has been particularly visible this year, as Blizzard phased out two of Hearthstone’s older expansions to create a new standard set for competitive play.

RNG is often treated as a monolithic quality, but Hearthstone actually employs many distinct types of randomness in its mechanics. Some cards allow players to influence their odds by modifying the board state. Other cards use randomness as a strength, providing situational versatility. Some cards become more reliable with careful deck construction, and others vary based on the opponent.

Fundamentally, randomness is created by picking randomly from a set. For example, a coin flip picks from the set of {heads, tails}. While each card interacts with randomness in a unique way, they can be broadly categorized by the set that they randomly pick from. In other words, the set of possible outcomes defines a type of randomness. We can use these categories to chart the evolution of randomness in Hearthstone through the years.

To begin, I need to limit the scope of my inquiry. Because Hearthstone is played with a shuffled deck, there is an inherent randomness in drawing a card. It could therefore be argued that Blackwing Corruptor (“if you’re holding a Dragon, deal 3 damage”) has an element of luck to it. For the sake of brevity, I will only be considering cards where a player with knowledge of the visible board state could not predict a card’s outcome in every situation.

Bluffing and hidden information are also outside the scope of this discussion. All of the “secret” cards in Hearthstone are triggered off of deterministic conditions, and are therefore not inherently chance-based. However, some secrets do have some randomness in their triggered effect.


Type - Coin Flip

A 50/50 coin flip is the most fundamental random game mechanic. Hearthstone employs it only sparingly, mostly as thematic flavour for clumsy ogres. Interestingly, pre-nerf Nat Pagle triggered at the end of turn, guaranteeing at least once chance for a card draw. This reliability made him a popular inclusion during the public beta, until he was adjusted.


Type - Random Target

Randomly choosing from the set of characters on the board is the most common type of randomness in Hearthstone. These cards should theoretically be more random than a coin flip, since “a random enemy” selects from an upper bound of 8 targets. In practice, these cards reward skillful play because players can modify the board state to favour their desired result; they’re more unreliable than they are truly random.

Deadly Shot destroys a random enemy minion, which in the worst case has a 1 in 7 chance of hitting the desired target. However, if the other minions can be cleared from the board, then the spell will have a single deterministic target. Cards that restrict their target selection by some characteristic (“Murloc” type or “with 2 or less attack”) further reduce the set of targets, providing players with even more control over the outcome.

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The Mystic Western Game Jam

Programming, Video Games

El Viaje Misterioso

Austin’s independent games collective Juegos Rancheros hosted another game jam this summer, and this year the theme was “mystic western”.

I hadn’t initially planned on participating, since I was already rather busy preparing for some summertime travelling. However, I was struck with a fun game idea that really fit the theme and scope. I wanted to make a game based on a specific scene from a 1997 episode of The Simpsons, where Homer hallucinates a mysterious voyage through a desert landscape under the influence of extremely spicy chili peppers.

For the gameplay, I took inspiration from the indie platformer Knytt Stories by Nifflas. It has a very clean, blocky, simple aesthetic that seemed feasible to imitate, even with my limited art skills. I also wanted to emulate its low-key pacing and its focus on exploration over combat. Having enemies to fight wouldn’t fit the vibe of the source material, where the mystic desert was mysterious but not threatening. Ultimately, I managed to translate almost every beat of the five minute hallucination sequence into some sort of playable experience (with the notable exception of the snake, which sadly was cut for scope.)

Mystic Western Jam - Notebook Sketches

Developing a platformer was also a good excuse to apply some of the lessons I learned from Steve Swink’s “Game Feel”. The book breaks down and analyzes the ways in which designers manipulate game physics in unrealistic ways to make platformers feel good. For instance, it taught me to increase gravity when the player is descending to avoid feeling floaty. I also implemented variable jump height, input buffering, and late jumping based on the lessons from this book.

You can download El Viaje Misterioso for Windows and OSX here:

Download from itch.io

Download (Windows)

Download (Mac OSX)

Source Code (GitHub)

At the end of the game jam, I was very proud to find out that my entry was one of the 25 games selected for the Mysteric Western Arcade at the Marfa Film Festival. I sadly couldn’t make it out for the event, but I hope people got a chance to play it there!

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Yharnam Metal Hypernym

Internet, Programming

To start off 2016, I thought I’d take a moment to write about some of the new Twitter bots I assembled last year. In my last post on the subject, I indicated that I was reluctant to continue making bots because it was distracting me from larger projects. However, since lately I’ve been focusing hard on a big exciting endeavour, I’ve found that making bots has continued to be a relaxing creative outlet in my downtime.

Yharnam Notes is a small tribute to Bloodborne, one of my favourite games of 2015. The game’s asynchronous multiplayer features include the ability to leave notes for other players using templates of words and phrases. These permutations can often be inadvertently lyrical, as Natalie Zed explored in her Bloodborne poetry. Inspired by this, I made a bot that constructs random messages using the vocabulary of the game’s note system.

Hypernym Bot was inspired by the folk proverb “For Want of a Nail”. I wanted to find a way to generate the same structure of text programmatically. Fortunately, Wordnik maintains a list of hypernyms (words that are more generic or abstract) for each word in their database. This made it simple to start with a random word, then iterate up the chain of abstraction of few times.

This is one of the silliest ideas that I’ve actually followed through on. Somehow my errant thoughts on @EveryWord and heavy metal clichés intersected, and led me to render every word in the English language in a heavy metal font. Tweeting a new word every four hours, @EveryMetalWord will complete its task by 2065.

You can find the complete list of my Twitter bots here. Wishing you all a happy new year, may your 2016 be programmatic and random!

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