Artificial Intelligence (abbreviated as "AI") in the Super Smash Bros. series refers to the intelligence of any Computer Player in the single-player and Versus Modes. In Versus Mode, players can preset the AI of a Computer Player. In Adventure Mode, All-Star Mode and Classic Mode, players can still set it to some degree.
Artificial Intelligence levels range from between 1 and 9, with 1 being the weakest and simplistic, and 9 being the most adverse. Beginners tend not to realize that the best way to practice against a Computer Player is to play a match against a level 1. The reason for this is that the higher the level, the more awkward and prone to spamming the play style will become. They also have much worse Directional Influence. Level 9 Computer Players fight like no human ever will, which gives the wrong kind of impression of practice. The best results are achieved by practicing combos against a level 1 Computer Player.
Criticism
There are many complaints surrounding the poor Artificial Intelligence of Computer players in Super Smash Bros. and Super Smash Bros. Melee. YouTube features several videos depicting the glitches in this faulty AI system.
Super Smash Bros.
Examples of flawed AI in Super Smash Bros. include Computer Players having poor recovery abilities and the spamming of the same, ineffective move in quick succession. Sometimes they don't even use their triple jump to recover, which can lead to a death.
In Hyrule Castle, a level 9 Kirby may repeatedly use Stone on the left side of the stage, sliding down, not cancelling it, leading to an early, quick death.
If there is a player on the right side of the Saffron City stage, Computer Players will walk into the doors of the Pokemon trap. When fighting Pikachu on this stage in 1 player mode, sometimes Pikachu will just walk down to his doom with you just attacking one time. There is also something simillar to that on Peach's Castle, where if a player stands on the bottom platform, and the CPU is on one of the moving platforms, it will run into the wall repeatedly.
When an item appears, a level 9 Computer Player will attempt to grab it, and will even stop fighting to get the item.
If a throwing item appears on a platform and a Computer Player picks it up and another player is below the platform, the Computer Player will throw the throwing item on the ground until it disappears, even if the item is a bob-omb, often leading to the Computer Player SDing.
If an AI player on any level is hit while, or even after using a third jump, it will never use it again until falling to it's doom, resulting in SDs.
There is an infamous AI glitch where if a player is fighting Fox in Sector Z, and runs off to the edge of the stage, Fox will follow the player and aim Fire Fox off of the stage, resulting in an SD.
Super Smash Bros. Melee
There are several examples of flawed AI in Super Smash Bros. Melee. Most Computer Players will use their neutral A attack and projectiles repeatedly, and are very easily edge-hogged. Certain stages are notorious for exploiting poor AI, such as Rainbow Cruise and Final Destination. Kongo Jungle is the best known stage for exploiting poor AI as it is easy to KO Computer Players by simply grabbing an edge, dropping from the edge as they attack, and then re-grabbing the edge. Another example of poor AI in Jungle Japes is to face a level 9 Ness on 1 stock and not move. The Ness will try to jump over to you, but will ultimately, fall into the river. Another example of poor AI is in Subcon, where if you are close to the left edge of the stage, a Level 6 DK will use his F-air or D-air then try to recover, but will ultimately SD.
The Computer Players in Melee also make poor use of their shields, and use grab attacks far more often than normal attacks. The best example is Dr. Mario. They also have a tendency to overuse one move, such as Captain Falcon constantly overusing Falcon Dive and Raptor Boost after forward throw, often in a self destruct when near the as well as Ganondorf spamming Dark Dive. Also, a computer controlled Luigi will never use his Up-B to recover, even if he is directly below a ledge, instead he will always use his side-B, which gains no vertical distance. Many Computer Players, especially while metal, will also self-destruct while attempting to meteor smash an opponent.Some CPUs in Melee will pick up a hammer on Jungle Japes. When a character with the hammer comes to a part where you must jump over the openings they will fall and not recover and be KOed. Sometimes they jump constantly swinging the hammer.
When an item appears, the Computer Players never picks them up (except healing items, Pokéballs, Cloaking Devices and Hammers), instead they only pick them up when the player or CPU are next to the items.
Super Smash Bros. Brawl
While the AI has been significantly improved, there remain some examples of AI limitations in Super Smash Bros. Brawl.
In Brawl, certain characters (most prominently Ness) know how to use their recovery more. Higher level Luigis will be resourceful. If a character gets an item like a Starman, rather than just trying to avoid that character, they'll also use the opportunity to attack any stragglers. When a Smash Ball appears, opponents will aggressively attack it at opportune times, while repelling anyone who tries to get it as well.
Another new feature is that the computer's level in Training Mode can now be selected. The AI is also improved drastically, as opponents set to Attack will actively fight the player, rather than walking towards them and rarely throwing an attack like in previous installments. One change from Melee is that Computer Players focus more on attacking human players rather than other Computer Players.
There are some examples of AI limitations in Super Smash Bros. Brawl. The CPUs seem to be somewhat easier to KO than a human player, even when set at level 9 (though, this was also present in the two previous games). They sometimes have hard time to avoid certain stage hazards, and sometimes self-destruct quite easily in certain situations in scrolling stages, such as Rainbow Cruise and Big Blue. They also generally have poor edgeguarding abilities, though, self-destructing while attempting to edgeguard isn't very common, unlike in the two previous titles. The flaws in Brawl's artificial intelligence are few, but potent. For example, when a player constantly grabs a ledge, the level 9 computer players tend to stand still until the player goes back on the stage and will sometimes self-destruct when attempting to attack the player. When a CPU Luigi uses Negative Zone, he will almost always spam his Fireballs over and over again, even on level 9, the same way that a Pit CPU using Palutena's army will spam his Palutena's Arrow (though, these were supposedly fixed for the PAL release of the game). When fighting against a level 9 Pikachu on Delfino Plaza, if one jumps in and out of the water while the Pikachu is on the land, the Pikachu will constantly use its down B. Some computer players may also play "stupidly" in very complex Custom Stages. In the underground versions of Mushroomy Kingdom, even a level 9 will sometimes repeatedly attack the blocks, ignoring the player even if items aren't on.
There has also been speculation that the AI at level 9 reads button commands and reacts accordingly, which has sparked anger among some smashers who feel that the AI should be made better rather than do what they term as 'cheating'. Some inconclusive experiments were performed by the SLAPAHO crew to see if this allegation is true, and though no definitive results were obtained, their findings justify future experimentation and research.
A CPU player (regardless of level) will always aim for solid platforms that can be sweetspotted when recovering, even when there are "soft" platforms off the stage.
There also appears to be a system in place which enables the AI to learn, as demonstrated in this video and this video.