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Yomi is the art of reading your opponents mind... in a very non-scifi fashion. This article describes the relevance of Yomi on both a player level (based on a linked David Sirlin article) and my own interpretation of how it can be implemented in design.
Yomi is a term that I feel should be more prominent in game design. ‘Yomi’, as interpreted by David Sirlin, is “the Japanese word reading, as in reading the mind of the opponent”. Sirlin uses this term as applied to games such as Virtua Fighter, which is a great example of Yomi, experienced through two players interacting. Player 1 can execute a move which sweeps the leg of his opponent. This move will be called ‘m’. Player 2 now has the ability to react if he’s predicted P1’s move correctly, by executing a counter, dubbed here as ‘c1’. This is where we are at first layer Yomi. P2 has predicted my move and reacted. P1 may have seen this counter coming, so P1 will run a counter to his counter, ‘c2’. This is an example of second layer Yomi. The moves can keep going back and forth, going deeper and deeper, but to make it easier on the developers, they made the initial move m counter c3.
So Many Levels...
In this example there are four layers of Yomi. Layer 0 is the initial move, where nothing was predicted. In Layer 1, P2 predicted P1. In Layer 2, P1 predicted that P2 would predict P1. In Layer 3, P2 predicted that P1 would predict that P2 would predict P1. Confusing, yes, and it may not be clear why this is even important in game design, but soon I hope it will make sense.
Yomi in multiplayer can fuel surprise and replayability. Yomi is a monstrous reason as to why Left 4 Dead works. In a game like Left 4 Dead, the ‘Versus’ levels are designed to give the special infected some great attack spots and other spots which gives the survivors a break. A novice player of Versus would travel through the level, not expecting anything, and just reacting to what is going on. Expert players, however, will use the principle of Yomi to fuel their pacing through the level. If the survivor knows that if they go out Door 1 they are vulnerable to a pounce from the Hunter (a special infected which deals loads of damage if he hits from a long distance away), they may send one person
out the door at a time, and have someone watch for the Hunter to counter the pounce. We are now at Yomi Layer 1. The Infected on the other side, know that the survivors will prepare for this attack. They set up a smoker (pulls the survivors towards the player from long distances) behind a fence to pull the player that will be watching for the Hunter. Yomi Layer 2. The survivors figure there will be a smoker there, so they send two players out Door 2 to flank the smoker. Yomi Layer 3. The Boomer (blinds survivors and attracts zombies) then attacks the flanking survivors as the Hunter pounces to prohibit the two survivors from killing the smoker. Yomi Layer 4. Left 4 Dead can go all the way to Level 7 or 8 Yomi, which makes the multiplayer so replayable.
Every time a new tactic is observed, it is added to your ‘Yomi Library’. This library is a collection of possibilities at a certain point in the game. Based on past experiences, players will anticipate and disregard certain assets in their Yomi Library. Once they play one move on Yomi Layer 0, the opponent is then forced to take something from his library that can counter the other players move. Sirlin goes into beginner’s luck and the reason for it in his article. 
Hunter Pounce
Experts can predict what another expert would do. Players will often say, “You need to think like your opponent”. In the above Left 4 Dead example, imagine that the survivors were all rookies to the game, and had an empty Yomi Library. Instead of advancing to Yomi Layer 1, they all run out the door at once. Since the Infected planned their moves, expecting to go to Yomi Layer 4, they are caught unawares and the survivors move through the section with barely a scratch. Eventually the experts will pick up on the novice moves and dominate them, but in the beginning they might not be so lucky. Experts will sometimes play like novices and attempt to throw a curveball at the Yomi system, breaking up the layers entirely.Yomi Interpreted for Game Development
Sirlin’s interpretation is on a player level, describing the interaction between two users of the game. I feel that Yomi principles are prominent in the relationship between developer and player. The developer needs to approach their game planning with Yomi for the player level. In this way, the developer is reading the mind of their target demographic. Using bases in psychology and anthropology, the creators can predict (hopefully) what most players will do in their game. Valve likely planned the Left 4 Dead levels to have certain level points geared towards survivor gameplay and certain level points focus on special infected gameplay. Virtua Fighter realized that they needed to implement counters, otherwise the game would be very encouraging of the famed button-mashing technique.
If a first-person shooter level is a big room with a few pillars and 16 spawn points, Yomi is blatantly ignored on the part of the developer. If the developer doesn’t consider it, then the player has no potential to use it. Good levels have believable environments, nice ambiance, and multiple paths to one area. Great levels fuel Yomi by giving players certain benefits to taking those different paths, and forcing teams to make decisions about which way to go.
Starcraft is another example of how Yomi can be fueled by the developer. Blizzard may or may not have expected players to use the infamous Zerg Rush against their opponents, but there is a way to counter it, which can leave the rusher in a very bad position. A developer must always make sure there are no un-counterable moves that could ruin one player’s experience. If this happens, one tactic will be used and every game will just be going through the motions, making sure you don’t make a mistake.
Tangent on Playtesting
Tangent
Level designers can prepare a game for Yomi by playtesting. I think in every blogpost I’ve had I have said something about testing or incremental development, but I feel it is with good reason. It is one of the most important things in creating a good game, and I will stand by that in every situation. By letting the player sit down with your game, you can observe tendencies, and how easy or difficult it is for them to pick up on the potential moves or paths you set up for them. I have been in a couple playtesting environments where the developer walks the tester through the game, saying, “Oh, over here is pretty cool, you can do this if you press this button and this button together”. This breaks the testing experience, and you can no longer judge that feature of the game. Wouldn’t it be cooler if with no prompt, your tester walked right over to your cool whatever and did it, then said for himself, “This over here is pretty cool!”. Anyways- back to Yomi.
Tangent’s Over
Using the tangent I described above, have your players sit down and play through the levels for a while. See if you notice any Yomi going on if your game is multiplayer. If there is, how many layers deep is it going? Are most players picking up on potential counters? Try t notice which testers seem to be experienced gamers. Are they taking certain risks or paths that a novice won’t attempt? This will fuel a gap between rookie and seasoned players. Is this gap healthy? (By healthy, I mean will the two levels of players be able to live in harmony? Will the rookie still be able to take down the veteran?) This following section will attempt to give some guidelines to follow for implementing Yomi into your game design.
Can each move by the player be countered?
Is it made clear to players that they can counter moves? If yes, is it an easy mechanic to pick up?
Can a counter be countered or blocked?
How many layers of Yomi can you get from single moves? Does anything happen as the layers get deeper and deeper (damage increase/decrease, time between attacks decreased)?
Is there any reason to break the Yomi layer chain? – Think about Left 4 Dead. Players can get a huge bonus by playing like a novice. They could run through an entire level and catch the special infected by surprise.
Are there certain paths in your level that have different benefits?
Are there any things that would make a player not want to take a certain path? Balance risks and rewards in your level, and make sure that there is always an equal balance (unless of course, you want a bunch of players to flock to a certain point, which would initialize Yomi).
If there is a point where most players will flock to, is there any reason not to go there? – Flanking is an example of this, or if one team flocks to the center to get something, the other team can collect all the other benefits elsewhere in the level.
As a player gets experienced with your level, are there certain things they expect an opponent to do every time? Between different playtests, are there any similar outcomes? If yes, there is potential for Yomi to be used in your game. If a player comes to expect something, his opponent will eventually expect that the first player will expect what he does (Layer 1 Yomi).
Are there certain reasons why players would advance faster through your level? Slower?
If a team moves quickly through a level, can the opponents react accordingly? Slowly?
Hopefully this article gave you some insight on what Yomi is and why it is important to consider in game development. Keep checking back for updates; now that the holidays have passed over I should have time to do a weekly post! As always, questions and comments are highly encouraged and welcomed.
Have anything to ask that you don’t want to put in the comments box? Want to get a discussion or debate brewing? Feel free to email me at [email protected], and I will get back to you as soon as I can.
http://www.sirlin.net/articles/yomi-layer-3-knowing-the-mind-of-the-opponent.html
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