Video games for Yu-Gi-Oh! have a particularly poor track record in this area. While some of the games' idiotic moves can be justified by the fact that the AI couldn't possibly know the identity of your facedown cards, and that the kind of analysis that would allow a player to even make the right guesses can be really difficult even for human players, some of the cases are a little more obviously Artificial Stupidity.
- In some games the AI will use an effect that requires paying life points when they have that exact amount of life points left. For example: AI has 800 life points, AI plays Premature Burial, AI pays 800 life points to use Premature Burial, AI immediately loses.
- Then you have Mokuba, for whom this trope is invoked intentionally. What a digital dummy! To give you the idea of how dumb he is, his second strongest monster is Kanan The Swordmistress, a normal monster with 1400 ATK and 1400 DEF (though to be fair, in the early games where the entire strategy was just summon low-level, high-attack monsters and overwhelm your opponent with them, 1400 ATK (and this was before Equip Cards) hurt quite a lot. He summons none of his monsters in defense mode, letting you just keep knocking them down. His entire strategy is to draw one monster, Cyber Stein, which has the ability to summon a fusion monster. This is the only way you can lose to him, because if he manage to do this, he'll summon Blue-Eyes Ultimate Dragon. Which he will gleefully prompt to crash and burn into your obvious Mirror Force/Sakuretsu Armor/Maneater Bug/Penguin Soldier/etc. Or even worse, into your more obvious Magic Cylinder, which will cause him to kill himself without failnote .
- In many of the earlier games, such as Eternal Duelist Soul, at harder levels, the AI essentially knew the ATK and DEF of any of your facedown monsters, and would make its decisions whether or not to attack based on that. Some of the "good" duelists like Yami Yugi go at you with cards that technically can destroy yours in battle...and then leaves them right open to a strong counterattack when the player is able to capitalize on the fact that they left a monster with 1000-1100 ATK in attack mode at the end of their turn. Attack! Attack! Attack! meets Artificial Stupidity here.
- The AI in Tag Force 2 is considered one of the worst examples of this in a Yu-Gi-Oh game, to the point where it seems like the game is actively trying to sabotage your efforts when you play a tag duel. A clear example came from a Tag Force 4 (video here)
, when the AI used Prideful Roar against Clear Vice Dragon. For the unaware: Prideful Roar pays LP to increase a Monster's ATK to be slightly higher than its target's, but Clear Vice Dragon's ATK is always double that of its attack target ...so it increases again when Prideful Roar activates. The AI paid 2800 Life, took more than double that in damage, and promptly lost. - The AI in general seems to have trouble with Monsters that can increase or lower ATK. For instance, say you've got Psychic Commander, a 1400 ATK monster that can lower the ATK of Monsters it battles, and the AI has Mystic Tomato, which has equal ATK and can Summon a weak Dark monster when destroyed. The AI is programmed to ram "searchers" into Monsters with equal ATK, so the AI will attempt to ram Mystic Tomato into Psychic Commander, then when that doesn't work, it'll Summon another Tomato from its Deck and do the exact same thing. It will repeat the process until it runs out of Tomatoes. One of the most infamous cases of Tag Force partner stupidity was this video. In a nutshell: The opponent, Para, had Suijin on the field. Suijin can, once per Duel, reduce the ATK of an attacking Monster to 0, so if you try attacking it, you'll lose your Monster and take a ton of damage in the process. Three guesses what the partner, Bastion, did, and the first two don't count. And Bastion is supposed to be The Smart Guy...
- Tag Force Special is the first game to feature Pendulum Summoning, and the AI simply does not know how to handle it. Yuya is by far the worst in this regard, with a near-insane aversion to putting his Pendulum Magicians in their proper spots and a refusal to use Entermate Wizard's effect. On top of this, the AI is set to always perform a strategy when possible, even when it's not a good idea. Pegasus is the most obvious offender, as this Duel shows. And even when they do have a workable strategy, they often don't use it; Kaiba will often Summon Kaibaman in ATK and then do nothing with it, even when he has a Blue-Eyes right there in his hand.
- Tag Force Special also reveals a rather large bug in the game's AI, since one of the Starter Villains from Yu-Gi-Oh! ARC-V, Eita, uses Ordeal of a Traveler. It makes your opponent guess the type of card in your hand whenever they try to attack, and if they fail to guess, their attacking monster gets bounced. The main trick with the card is remembering the cards in your opponent's hand... something that the AI simply does not do. Even when Eita has one card in his hand, he's revealed it to be a monster four times, and he hasn't played any other cards, your tag partner will continue to rush in, guess "Spell Card!", and get all your cards bounced.
- In Yu-Gi-Oh! Dark Duel Stories, the A.I.s have a bad habit of offering high-ATK monsters as tributes to summon something of the same strength or even weaker, example: Offering "Jirai Gumo"(2200ATK/100DEF) as a tribute to Tribute Summon "Catapult Turtle" (1000ATK/2000DEF). The AI also likes to use monsters who have lower ATK than DEF to attack, as long as the ATK is at least half the DEF. Sometimes, Yami Yugi will use "Megamorph" (which acts like a universal Equip card, increasing a monster's ATK and DEF by 500) on Mystical Elf just so that he can attack... with 1300 ATK.
- There's also its inability to judge the worth of cards in its hands, meaning that it discards randomly whenever an effect makes them do so, which can often make them cripple their entire strategy by eliminating their most important card. To wit: The AI has three cards, which consist of a weak monster, a strong monster whose level is too high to be summoned, and a spell which makes the user discard a card but would let him summon the stronger monster. The AI will, 50% of the time, activate the spell, discard the stronger monster, and then summon the weaker monster which wouldn't need the spell in the first place.
- Yu-Gi-Oh! 5Ds's Duel Transer/Master of the Cards is also not immune. The AI Computer opponent you have unlocked initially has a few decks that are easy to overcome, but for some reason it likes to set off a combo of Waboku and Hallowed Life Barrier. Waboku stops you taking damage that turn and stops your monsters from being killed, Hallowed Life Barrier is basically the same, except you need to discard a card to activate it, and all it does is nullify battle and effect damage, not protect monsters.
- The AI is incapable of deciding whether or not using particular traps is a good idea or not. If your opponent has Torrential Tribute set (a trap which wipes all monsters on the field when activated), they'll use it even if the monster they already have on the field is stronger than the one you just summoned.* Opponents using Torrential Tribute to destroy the whole field when they have a 2500+ ATK ritual monster out when all you did was summon a relatively weak monster is common enough to count as a strategy to get rid of their monsters.
- Not to mention that they will tribute summon their powerful monster, and then play Torrential Tribute, wiping out everything. Also done with Dark Hole.
- Despite being the main character, Yugi will often make the baffling decision to keep summoning Sinister Serpent, an effect monster with 300 ATK and 250 DEF. It's effect is to keep showing up in his hand if it's destroyed. Good if you plan on sacrificing it, but he never does this. He keeps it out until you vaporize it with a much stronger monster, and then keep summoning it just because.
- Total Defense Shogun is particularly weak in the hands of the AI. It has 1550 ATK, 2500 DEF, and it can attack while in defense mode. Whenever they play/use/control one however, they will always switch it to attack mode. So, basically, the AI weakens the monster by 950 points, AND opens themselves up to Life Point damage voluntarily.
- The AI will sometimes use Premature Burial or Call of the Haunted to summon Gearfried the Iron Knight. Either of those cards can be used to summon a monster from the Graveyard, but the card is then equipped to the monster; if the card is destroyed, so is the monster it summoned. Gearfried destroys any card that is equipped to it automatically. Yeah... Even more humorous because Premature Burial costs 800 life points to use.
- The AI has also been known to do things like take control of your monster using a card like Change Of Heart, which takes yours for one turn, but then boost its stats with a permanent equip spell. So at the end of your turn, you get your monster back, only the AI has actually helped you. Similarly, it's a common player strategy to Suicide Attack a weaker Monster into a stronger one, because the weaker Monster has an effect that activates in the Graveyard (see: Sangan, Mystic Tomato). The AI will do this with Monsters they've taken control of, even though cards revert to their owner's control in the Graveyard - so if an AI attacks with a stolen Sangan, it goes back to your Graveyard and YOU get the effect while they take damage. Thanks, buddy!
- In Yu-Gi-Oh!: Dungeon Dice Monsters, any character not found in the anime will just summon around their Heart Points and will eventually use up all their summons. They will then be unable to do anything, allowing you to have as many rolls as you need to summon anything. The Exodia pieces can be summoned this way, and by summoning them all, you get an instant win, and the AI is powerless to stop you. You can beat anyone in the game with an equally inane strategy. There are summonable "items" in the game which take the form of chests. Only the summoner knows what's in the chest, and it activates when a monster passes over it. The AI will never run over your chests, in the expectation that it might be a trap (and, to be fair, it might). However, it is possible, by spamming cheap summons, to block your opponent so that the only path to your heart points is through the chest. At which point, the AI will helpfully sit around, waiting for you to kill them. Also, the AI will never attack your monsters unless it can one-shot-kill the monster, and usually not even then. The AI will never use its own items even if they're beneficial, so you can use their items to power up your monsters or even revive your destroyed monsters. The AI will never use its monsters' special effects (the sole exception being Orgoth the Relentless) even if they have the crests to do so. You can be right next to the enemy's Die Master getting ready to secure the winning strike, and the AI still will not attack your monster or attempt to protect itself. Again- with rare exceptions. The AI will also head straight for your die master and get stuck in corners and dead-ends as a result. The AI will even select dice that make it physically impossible for the AI to summon a monster.
- Macro Cosmos Decks turn most games against the AI into a comedy of errors. Macro Cosmos removes any card that would enter the Graveyard from play, meaning that many strategies centering around the Graveyard become fairly crippled. A human player would attempt to destroy Macro Cosmos as soon as possible, then initiate their normal strategies. Not the AI, which will completely ignore Macro Cosmos and continue to play as if it wasn't there. You haven't seen Artificial Stupidity until you've seen an AI use Foolish Burial to remove its own Treeborn Frog.
- Oftentimes, there'll be at least one character who plays an Exodia Deck. Exodia is an infamous set of cards: five weak Monsters that, if you hold all five in your hand, let you instantly win the Duel. A human player will try to protect the pieces at any cost, not Summoning or discarding them unless they have a way of getting them back - if you lose a piece, it's game over, since Exodia Decks usually feature little beyond drawing cards and maybe defensive cards. The AI has no such qualms, perceiving them as only weak monsters, and will regularly ditch the pieces at the first opportunity. The worst part is when you've got a clear field and the AI decides to summon a 200-ATK Left Arm of the Forbidden One to attack you.
- Yu-Gi-Oh! Reshef of Destruction mainly averts this, due to having a much simpler ruleset that's harder to screw up, but the computer will always attack your cards if they are face down in defense mode unless their monsters have 0 Attack. This will happen even if you use a card to cover up previously seen monsters.
- An app called Yu-Gi-Oh! Duel Generation generally has incredible AI., but Pot of Duality seems to cause some hiccups. Instead of taking something useful like Mirror Force, they'll take Skelengel. They also take a Field Spell card when they already have the exact same card already on the field instead of a monster to defend their life points.
- Yu-Gi-Oh! Destiny Board Traveler has this when the Outer Space board is used. The AI will heavily prioritize summoning monsters, and generally ignore the special spaces, which is a very bad idea on this board, since if a player doesn't go to a special space for 5 turns, they will lose 1000 Life Points. It is very possible to win on this board with this being the only way your AI opponents take any damage at all.
- In Eternal Duelist Soul, the AI doesn't know how to use Special Summons correctly. Mai has a card in her deck called Elegant Egotist, which allows her to Summon a Harpie Lady or a Harpie Lady Sisters from her hand or deck, as long as there is already a Harpie Lady on the field. Harpie Lady Sisters has 1950 ATK and 2100 DEF, and can only be summoned through Elegant Egotist's effect, while the regular Harpie Lady has 1300 ATK, 1400 DEF, and no effect or summoning conditions. Mai will always play Elegant Egotist and choose to bring out a second Harpie Lady, even if the player's Monsters have more than 1300 but less than 1950 ATK, and therefore makes one of her cards a total waste of space. Similarly, Yami Yugi will never Summon Valkyrion the Magna Warrior.
- At least in Worldwide Edition 2004/Stairway to the Destined Duel, the AI likes to changes its cards to defense mode if it can't make any meaningful attacks. It'll even do this for cards with higher ATK than defense, leading to cases where a card, especially hard hitters with low defense like Gemini Elf (1900/900), Vorse Raider (1900/1200), or to a lesser extent St. Joan (2800/2000) will be left open to getting splattered when it would've been safer had it stayed in attack mode.
- In the same game, Strings has an odd quick where he likes to play Jam Breeding Machine (which makes him place a Slime Token each turn, but stops him from summoning anything else) without doing anything to back it up, effectively putting a huge target on himself since he's unable to move them to defense mode the same turn they appear, letting you merrily crush them with impunity.
- In games where Weevil is an opponent, he's known to run Cockroach Knight, a card that returns itself to the top of the deck when destroyed. If you destroy it, it'll return to the top of his deck, and then he'll draw it and play it again, ready to be destroyed again. Effectively, he locks himself into drawing the same useless monster, forever.
- The AI tends to prioritize dealing damage to the opponent over everything else. This is especially noticeable in the games based on the Dark Signer arc of 5D's, as a large number of duelists run cards that have the ability to attack the other player directly. For example: the AI has a 3000 ATK monster that can attack directly, and 2000 life points, while the player has 5000 life points and a 2000 ATK monster that can also attack directly. Any human player would attack the monster so that they can't be killed on the next turn, but the AI will instead attack directly, setting themselves up for defeat.
- AI characters that use Dark Bribe (negate a Spell or Trap but lets your opponent draw a card) to block the effect of your Upstart Goblin (you draw a card and your opponent gains 1000 LP). So they stop you from drawing a card, and in exchange, they lose a valuable Counter Trap, don't gain 1000 LP... and then you draw a card.
- Yu-Gi-Oh! Duel Links: The auto-dueling feature can make very dumb moves at times, as can the AI.
- Yugi's Level 40 deck revolves around spell counters, which he usually uses to power up his attacking monsters even when you've used Mask of Accursed to stop them from attacking. In some cases he'll use Wonder Wand to destroy the monster even if it's powered up to draw 2 cards.
- Mai's Level 40 deck revolves around Amazonesses, including Amazoness Chain Master. If it's destroyed and she has enough LP, she will use it to steal a card from you even if it's worthless. What makes this one stand out is that she has to pay a 1500-LP cost to make it happen; hardly a small price in a game where both players start with 4000.
- Para and Dox's Level 40 deck revolves around Kazejin and Suijin. Since their effects only work once per duel and the AI has no way to track this, they'll tribute a Kazejin and Suijin to summon another Suijin, even if you have a weaker monster than both of them.
- After the 1.7 update, Yami Bakura gained the habit of playing Malice Doll of Demise in Attack Position even when your monsters are stronger. The intent is to combo it with Ectoplasmer, but the problem is that he plays it even when Ectoplasmer isn't out.
- Syrus Truesdale's Level 30 and 40 decks has Inverse Universe, a card that swaps ATK and DEF, which for whatever reason, he may activate even if it does not change the situation at all (the attacking monster still destroy his monster anyway, despite the change in stats). He also sometimes sets a monster in defense mode and then automatically destroys it with Shield Crush.
- In her event, Anna Kaboom makes liberal use of Night Express Knight, a monster that can be summoned without Tribute at the cost of its ATK becoming 0. The intention of this effect is to summon Rank 10 monsters like her ace Gustav Max, but as an AI, Anna has a tendency to summon Night Express Knight and then immediately end her turn, giving you a free shot at her Life Points.
- Black Dragon Ninja has an ability to banish any opposing monster for the price of a Ninja monster and Ninjitsu Art from your hand or field. However, this comes with a drawback; if Black Dragon Ninja leaves the field, it will Special Summon all those banished monsters back to the field. If there are no other Ninjas, the AI will sacrifice Black Dragon Ninja itself, ignoring the fact that doing so would cancel its own effect out.
- The Auto-duel AI hit a big snag around the release of Blades of Spirits as it's gotten way weaker/dumber. Such maladies with auto-AI include occasionally giving purely beneficial equip cards to your opponent's monsters, just plain not using cards, summoning monsters like Sphere Kuriboh (weak monster that works better as a hand trap than being summoned) or Labyrinth Wall (zero attack) in attack position, and using cards like Enemy Controller on things when there's no need to or it puts you in a worse situation. Considering the opposing AI never does this, it's clear that the auto duel AI was intentionally designed to be worse.
- Tag Duel partner AI seems fine enough, but only when using their own cards. If you have specific strategies involving said card, chances are, the AI partner will misuse the card. Although, they're not prone to being stupid in other ways as well, such as Kite tributing a perfectly good Galaxy-Eyes Photon Dragon to summon another Galaxy-Eyes Photon Dragon.
- Against a Karakuri deck, they'll constantly attack you even if you have a facedown card that can turn the tides in your favor because of the effect of those monsters shifting them to defense mode. They'll walk right into all of your spells and traps easily. Note that this is largely because most Karakuris have effects that force them to attack if possible, so the AI isn't entirely to blame here... until you see one summon a weak monster like Ninishi (which has 0 ATK) in Attack Position and then just leave it there when they start their Battle Phase.
- NPCs in general seem to have an issue with cards that mill their own deck - they will use the card's effect just to reduce damage once or destroy 1 monster, regardless of the risk in accidentally milling important cards. They will also continuously spam the milling effect if possible, even if they end up doing nothing else on the same turn due to still being unable to break your board. This can result in them needlessly cutting their deck until they have only 4 or even 2 cards left, making it easy for them to Deck Out if you just stall for a bit more. Similarly, they will also keep spamming draw effect when possible, stopping only if their deck has less than 5 cards left, making it easier to Deck Out them.
- Auto-dueling will also not use abilities even when the criteria fits, even when doing so could help them turn the duel around.
- Yu-Gi-Oh! Cross Duel has AI that finds ways to misuse pretty much any Spell Card they manage to draw. Give them a position changing card, for instance, and they'll proceed to use it to switch a monster that's about to be destroyed into its stronger battle position or prevent an opponent from taking damage (this also happens with Shield and Sword, which they often use to effectively make an enemy monster stronger). It doesn't help that they often seem to choose targets at random, leading to, say, Yami Yugi using Swords of Revealing Light or Block Attack on some random monster halfway across the board instead of one that's about to attack for game.
