For this article, I'll discuss mixups in general barring the learner's mixup. The Learner's mixup has very little to do with a game's design and everything to do with the way players think and learn. Because it's so personal, we can leave it aside for now. For this article, we'll look at a few design features in games that can facilitate mixups.
moves that commit players and limit player options
Mixups are all about influencing a player to make mistakes with their choices. It's the choice that can be right or wrong and be followed up with serious consequences. For any given mixup, if the player could test an option of the mixup while playing it safe, then it's much less likely for that player to make a mistake in the first place. In other words, if the point of a mixup is to land a player in jail and they have a "get out of jail free ability" the mistake the player may make can be nullified. Video games are about interactivity, which means cause and effect. To make the effect more meaningful the cause must be linked.
Mario is committed to player actions through gravity and momentum. What goes up must come down. An object in motion tends to stay in motion unless acted upon by an outside force. In Mario's case, coming down can land players in trouble, and that outside force can be colliding with an enemy. It wouldn't be much of a game if you could play it safe all the time. Take the P-wing for example. Infinite flight with the P-wing in SMB3 is a rare powerup that removes much of the game or challenge away from a level by allowing players to fly over everything and play it safe. (Quote from Iwata Asks)
NAKAGO: But if we'd simply gone with Tezuka-san's idea as it stood, Raccoon Mario would have been able to stay in the air and fly straight to the goal. That would have been ridiculous.
IWATA: If Mario can just keep flying about, you couldn't really call that a game. (laughs)
canceling moves
In the same way that two similar looking moves can create a mixup (look-alike/with tell), being able to cancel a move can facilitate similar mixups. For cancelable moves, instead of committing to one move you can change a move to a variety of other moves and options. So when a player sees the first move they may think that you're committed to it when in fact you can change it. Designers must be very careful when designing cancelable moves. If there are too many cancels the base level flow of the action created from move commitment will weaken.
The focus attack in Street Fighter 4 is one move with a myriad of applications. The attack itself can absorb 1 hit of an enemy attack and break through blocks when fully charged. These attributes make the move quite formidable but not unbeatable. 2 hits, a grab, or special focus breaking attacks counter focus attacks. With so many ways to be successful and unsuccessful using focus attacks, canceling the focus attack can become an effective mixup. Instead of committing to the whole attack, you can cancel it by dashing backwards or forward. By feigning an aggressive play, you may be able to bait the opponent into falling for your defensive trap. Or just when your opponent anticipates that you'll cancel the focus attack with a dash, you can give it the full charge. See this match video for some high level play and lovely mixups.
gameplay speed
Competitive gamers especially love to play it safe. If they can confirm success of a choice before making it, they'll do so. Likewise, such players often like to play games as safely as possible. This means guessing as little as possible and throwing out as few risky/random moves as possible. Competitive action games are often developed to play at a certain speed to reduce and balance the effectiveness of quick reflexes and playing it safe with other interesting styles of play.
Gameplay speed refers less to the frames per second and even character movement of a game(when characters apply), and more to the amount of time a player has to successfully react to elements of contrary motion. For a game like Mario, Goombas and other enemies move very slowly (and predictably) giving the player plenty of time to see and plan around them. However, Mario is a game designed in counterpoint layers. This means the time you have to react to elements changes based on the type/number elements on on the screen and how fast Mario moves.
Fighting games are very different. In a 1v1 fight, the main obstacle is the other character/player. The speed of attacks are generally too fast to react perfectly too. Simple punches in Smash or Street Fighter can come out 5/60th of a second after the button is pressed. Some attacks happen much faster at 1/60th of a second. In general, the trade off is between speed and power. Jabs are weak, very quick attacks. Smashes/Fierce attacks are slower, but much stronger.
If such an action/fighting game moved in slow motion, fast and slow thinking players would be brought to a closer level. And if you remove time altogether, like with many turn based games, you eliminate the importance of timing and reflex skills completely. With these games players have all the time they need to study the game, recognize moves, spot tells, and play it safe.
Bring a fighting game back up to speed and the time the player has to spot tells and plan accordingly gets reduced and even eliminated. You can't react to a 1 frame attack. By the time you see it, it's already over. With such a design players lose the option to play at their own pace and think everything through while gaining new opportunities to catch the opponent off guard. Because moves are so fast and the actions of the game keep flowing without pausing, often times a defensive stance is a player's safest tactic. You may not know what's coming at you, but at least blocking/shielding will stop most attacks and hopefully buy you some time to think. Putting up a defense usually gives the aggressive opponent the advantage allowing them to use attacks, push you around, chip away at your defense, and possibly counter grab all without the threat of being attacked back. In this way, offensive play can be privileged over safer, defensive play styles. For these games, fortune favors the brave and it takes guts to be amazing.
blindness
The double blind mixup described in part 1 of this series is a specific type of mixup in the broad category of blind mixups. Blind mixups occur whenever a player makes choice in a situation where crucial information is obscured when there are right and wrong choices to make. Having a percentage chance of missing an attack does not qualify. Examples include calling a coin flip (50%). Guessing right in RPS (33%). Or finding the hidden character under one of the magical hats (25%). These are all examples of one player not being able to perceive all the factors at play and being influenced to make a choice playing against the odds. Fog of War can blind players and create mixups as well as limiting camera perspectives.
Mixups are a very important part of fighting games. A fight using martial arts is not a concept created for video games. Such fighting has existed for thousands of years. Fighting games are designed to simplify and abstract the art. Like with many real life sports and physical activities there isn't a single move or strategy that can win in all situations. And even if there was one, human endurance and execution play a factor. For these reasons, a fight is often won or lost not because a move, play, or a strategy is unbeatable, but because it was used in a broader way to out smart the opponent. In a situation where the opponent is the main obstacle, overcoming him/her is the only way to win. And however you reach that goal is legitimate (assuming you play by the rules) even if you have to get inside their head and trick them.
I'll conclude with a few extra terms.
Oh, and if you're the type of reader who was confused by the article title and searched through the blog (possibly through the archives) looking for pt.2.... consider yourself mixuped.