History ObviousRulePatch / YuGiOhCardGame

* In ''VideoGame/YuGiOhMasterDuel'', one of the first event hosted in the game was an [=Xyz=] festival that forced players to use only [=Xyz=] monsters, banning not just non-Xyz Extra deck monsters but also archetypes that don't revolve around Extra deck plays such as Eldlich and Monarchs to prevent players from cheesing the event. To encourage players to participate in the event, players are awarded points even if they lost the duel (100 for winning & 50 for losing and none at all if they surrender). However, players soon found out that it was far more efficient to lose twice in quick succession than to play a legitimate game that could last up to 15 minutes, thus this caused most of them to run self-burn decks that was designed to quickly deplete their own LP as fast as possible in order to attain gems as efficiently as possible, with only little investment required compared to the cost of building a competent Xyz deck. As a result, Konami increased the reward for winning from 100 to 500 in order to incentivize legitimate Xyz duels. Subsequent events such as [=N/R=] and Synchro Festivals flat-out bans any cards that purposely deplete your LP as fast as possible while still keeping the greater reward for winning in order to deter any further self-burn decks in the events.

* With the release of Xyz Monsters, there was a brief period where there were very few written rules about how they actually work - one key problem was the fact that the monster used for Xyz Summoning visibly stayed on the field until "detached" by an effect. Fine, but when do effects that specify when a monster "leaves the field" trigger? [[WordOfGod Kevin Tewart, head of development for the overseas TCG,]] said that they trigger on Xyz Materials being detached, and ''all hell broke loose''. Two already powerful cards got so absurdly broken that a single copy could easily fetch well over 100 dollars. Konami quickly made a rule change to have the TCG rules coincide with the Japanese OCG rules: Xyz Materials are not treated as if they were on the field, ''but effects that activate when they "leave the field" do not trigger when a monster becomes an Xyz Material''. It's just as weird as it sounds.
** These two cards were "Sangan" and "Tour Guide from the Underworld", along with any given Rank 3 (at the time, Number 17 Leviathan Dragon was favored). The combo is this: Tour Guide is summoned, whose effect summons a level 3 Fiend-type monster from the Deck, at the cost of negating that monster's effect. This monster would be Sangan. They overlay to form Number 17, whose effect is to "detach" a card to become stronger. The effect negation of Tour Guide is now void, since Sangan's state has changed. Number 17 detaches Sangan to become stronger, and Sangan's effect activates. After the ruling was clarified, this was no longer possible. That said, cards that activate when "sent to the graveyard" will still activate - just not the ones that require being sent from the field to the graveyard.

* "Once per turn" restrictions were as written -- you could use the monster's effect once per turn while it stayed on the field. However, should that monster leave the field and return, or if you got another copy of that monster onto the field, you can use that effect an additional time. Clever use of Summoning loops led to players getting way more mileage out of these effects than the designers intended. Now, you're more likely to see the phrase "You can only use the effect of (card name) once per turn", closing the loophole for most effects, especially the more potent ones.

* In early 2015, a card-specific rule patch was introduced: "Dark Strike Fighter", a card banned mere months following release given its ease of summoning, high attack, and powerful burn effect, had the latter effect limited to Main Phase 1, and only once per turn, period.
* As of the 2015 change to Dark Strike Fighter, Konami announced a new stance regarding forbidden cards. Now, every so often they would introduce several [[http://yugioh.wikia.com/wiki/Errata errata]] by changing card text to one or multiple cards on the Forbidden List. Notable examples are Crush Card Virus and Ring of Destruction. The overriding sentiment is, it's better to make a card weaker and actually usable than keep them as strong as they are originally and have them remain on the list forever.

* A German player, Maik S., [[https://www.youtube.com/watch?v=Ns17sYK4Eag entered the 2007 German National Tournament with a 2,222-card Main Deck and 222 card Fusion Deck]], as part of a joke with a friend. Maik, himself an official judge for Upper Deck Entertainment (the company running the tournaments), knew there was only a minimum deck size limit for the main deck or the Extra Deck (then known as the Fusion Deck), without a maximum. The deck used was practically impossible to shuffle effectively, could not have easily verified contents, and [[https://yomifrog.lima-city.de/2222_card_deck_ygo/index.php?lang=en used a specially constructed hand that could be seen from several tables away.]] After the first duel, the event's chief judges convinced Maik to drop out of the tournament. In less than 1 year, the first ever standardized "Master Rules" format introduced a restriction on deck sizes to 60 cards, and a restriction on Fusion (Extra) Deck size to 15 cards, limitations that have stayed in place to this day. This occurence at a national event may have led to this rule being put in place.

* Most of the new Monarchs Spell and Trap support require that the player have no cards in their Extra Deck to trigger their effects. One of the most prominent among them is [[https://yugipedia.com/wiki/Domain_of_the_True_Monarchs Domain of the True Monarchs]] where it can lock out the opponent of special summoning their Extra Deck in addition to the player controlling a Tribute Summoned monster. However Monarch players tend to deceive their opponents by placing cards in the intended Extra Deck before revealing that it isn't actually part of the deck which led to ruling hassles and declarations of unsportsmanship conduct. Shortly after Emperor of Darkness Structure Deck was released in the TCG, a player's Extra Deck is now public knowledge even before the duel has started and players must truthfully respond whether or not they have any cards in the Extra Deck if asked.
* In ''VideoGame/YuGiOhMasterDuel'', one of the first event hosted in the game was an [=Xyz=] festival that forced players to use only [=Xyz=] monsters, banning not just non-Xyz Extra deck monsters but also archetypes that don't revolve around Extra deck plays such as Eldlich and Monarchs to prevent players from cheesing the event. To encourage players to participate in the event, players are awarded points even if they lost the duel (100 for winning & 50 for losing and none at all if they surrender). However, players soon found out that it was far more efficient to lose twice in quick succession than to play a legitimate game that could last up to 15 minutes, thus this caused most of them to run self-burn decks that was designed to quickly deplete their own LP as fast as possible in order to attain gems as efficiently as possible, with only little investment required compared to the cost of building a competent [=Xyz=] deck. As a result, Konami increased the reward for winning from 100 to 500 in order to incentivize legitimate [=Xyz=] duels. Subsequent events such as [=N/R=] and Synchro Festivals flat-out bans any cards that purposely deplete your LP as fast as possible while still keeping the greater reward for winning in order to deter any further self-burn decks in the events.

* Lists in game started as just the Limited List: normally, you can have up to three of any one card in a deck, but for game balance reasons the Limited List mandates that only one (Limited) or two (Semi-Limited) copies of certain cards can be included in a deck. Before long, players were discovering interesting ways to break the game using card combos the game designers hadn't foreseen, resulting in absurdly powerful decks that could force a win in a single turn (or even the first turn). Thus the Limited List was expanded to include Forbidden Cards, which cannot be included in a deck at all. The list is changed roughly every six months, with cards being both added to and sometimes removed from it.
** And even then, on occasions where a Deck outright dominates a tournament scene, the "emergency banlist", not restricted by such a schedule, can be enacted to knock the dominant Deck down a notch.
* In an interesting take on this, the formerly-Limited card "Twin-Headed Behemoth" was taken off the list because of a ruling change: Its effect (which lets it revive itself from the Graveyard at the end of the turn it's destroyed from the field with 1000 ATK and DEF) specifically states it can only be activated "once per duel". It was put at 1 after it was pointed out that multiple copies of the card would make it impossible to keep track of which copy had used its effect and which haven't, meaning anyone could abuse the confusion and reuse the card's effect illegally. Now, though, the card's ruling has changed so that only 1 copy of it owned by a player can activate its effect per duel, period. The rule change was completely arbitrary, only allowing the card to become unlimited without interfering with the reasons it was limited in the first place. A similar case happened with Treeborn Frog, which won't activate if one is already on the field, allowing it to be unlimited.
* The worst examples of this in Yu-Gi-Oh are Yata-Garasu and the two Envoys. Nearly all of the other cards on the Forbidden list are pivotal in combos. These three cards were banned just because they were ''[[GameBreaker that broken.]]'' Not helping the Envoys' case is a rule known as priority, which allows the player to activate their effects (which can normally only be activated at times when the player could activate a Normal Spell) immediately when they're Summoned, before the opponent has the chance to activate cards that would destroy them. Following the introduction of the Xyz monsters in the game, the OCG and TCG had their priority rulings patched to prevent people from calling priority on Ignition monster effects. Black Luster Soldier - Envoy of the Beginning has since been taken off the list. Chaos Emperor Dragon required errata to undo its banning: the player cannot activate any other card effects on the turn its nuke is used, and the damage is only done with respect to the opponent's cards that are sent to the Graveyard. Of the three cards, only Yata remained banned for a long time (The latest banlist made it Limited). [[note]]Yata-Garasu was a 200 ATK spirit monster that made the opponent skip their next draw phase whenever it connected. Because it bounced itself at the end of turn, it was effectively immune everything other than Quick-Play and Trap cards, so if it got through, and you didn't have an answer that very second, you almost certainly lost the game. and you have to sit there and take 200 damage each turn and hope he milled out before he killed you. [[/note]]

* Also, the "Archfiend" cards, an issue resulting from {{bowdleriz|e}}ation of card names. In the Japanese version, several cards used the word "Demon" in their names, and this word was changed into a bunch of different words in the initial American releases: "Demon's Summon" became "Summoned Skull", "Demon's Axe" became "Axe of Despair", and so on. This worked fine until a series of cards that specifically dealt with cards with "Demon" in their names started to come out, so a ruling had to be issued to declare "Archfiend" as a "special category of card" which included all the cards that had "Demon" in the Japanese name. From then on, "Demon" would always be translated as "Archfiend". Later on, new printings of the Archfiend cards would include rules text stating that they were treated as Archfiends at all times, even on the Normal Monsters.

** These two cards were "Sangan" and "Tour Guide from the Underworld", along with any given Rank 3 (at the time, Number 17 Leviathan Dragon was favored). The combo is this: Tour Guide is summoned, whose effect summons a level 3 Fiend-type monster from the Deck, at the cost of negating that monster's effect. This monster would be Sangan. They overlay to form Number 17, whose effect is to "detach" a card to become stronger. The effect negation of Tour Guide is now void, since Sangan's state has changed. Number 17 detaches Sangan to become stronger, and Sangan's effect activates: when it is sent from the field to the graveyard, it adds a 1500-ATK-or-less monster from the Deck to the hand, such as another Tour Guide. So, to summarize, at no loss of hand advantage (a very important resource in Yu-Gi-Oh), you have a 2500 ATK beatstick facing your opponent down. This is no longer possible due to the new ruling. That said, cards that activate when "sent to the graveyard" will still activate - just not the ones that require being sent from the field to the graveyard.
* "Light and Darkness Dragon" has so much text on it that Upper Deck/Konami never fit a very important sentence on it: its negation effect can only activate once per chain. If Konami had never announced that ruling, Light and Darkness Dragon would continually keep activating to negate ITSELF until its attack and defense got so low that it couldn't activate any more. This ruling also gives Light and Darkness Dragon its main weakness, which is that a card can be chained to its effect, which it will be unable to negate.
* In early 2015, a card-specific rule patch was introduced: "Dark Strike Fighter", a card banned mere months following release given its ease of summoning, high attack, and powerful burn effect, had the latter effect limited to Main Phase 1, and only once per turn, period. Sadly though, with the attack and burn for OTK shenanigans largely curbed, most fans decried it as a JokeCharacter whose role as a reliable level 7 Synchro was completely outclassed to the point that it became Unlimited after its errata and has been forgotten from the metagame ever since.
* On occasion, Konami/Shueisha have been known to create less overpowered counterparts or cards performing similar functions as replacements for cards retired to the Forbidden list either before or after the fact - Tradetoad for Substitoad, Rescue Rabbit for Rescue Cat, Fishborg Launcher for Fishborg Blaster, Demise, King of Armageddon, Ruin, Queen of Oblivion, and Sky Scourges Enrise and Norleras for the Envoys, being notable examples.
* As of the 2015 change to Dark Strike Fighter, Konami has taken an interesting stance. Now, every so often they introduce [[http://yugioh.wikia.com/wiki/Errata errata]] by changing card text to one or multiple cards on the Forbidden List. While before they were just rule patches, as of Dark Strike Fighter and beyond they're doing it simply to curb the power of certain cards. Notable examples are Crush Card Virus and Ring of Destruction. The overriding sentiment is, it's better to make a card weaker and actually usable than keep them as strong as they are originally and have them remain on the list forever.
* Several cards that were released starting from [=ZeXal=] era have been given an "only once per turn" rule because many pro players abused infinite loops and lack of once per turn restrictions to form easy one-turn or even first-turn kills. In fact, one player even managed to win a world championship by using a Frog FTK deck, leading it to be completely neutered by the following banlist.
* Following Link-climbing shenanigans involving Crystron Needlefiber, Isolde, Two Tales of the Noble Knights, and Summon Sorceress, several Link Monsters capable of field swarming introduced in later sets are unable to be used as Link Material the turn they are Link Summoned, specifically require an in-archetype monster to be used as Link Material or restricts on what monsters that can be special summoned. Additionally, starting from SEVENS era, many of the introduced archetypes that does not revolve around Link Summoning severely restricts the player from special summoning or activating effects outside of their designated archetypes.
* After cards that easily Special Summoned multiple Token monsters like Dandylion or Grinder Golem got themselves on the banlist for providing easy Link Material for Link climbing shenanigans, subsequent Link Monsters would specify their (otherwise generic) Link Material requirements as either non-Token monsters, monsters with different names, or both. Subsequent cards that churns out easy Tokens now either prevents them from being used as Link Materials or restricts the player from Link Summoning for the rest of the turn.

** The deck, which was practically impossible to use effectively, included effects that would require the deck to be shuffled afterward. As this would take a very long time to be shuffled, judges ruled him out of the tournament as it could cause games to take a very long time and thereby hold up the entire tournament. It was also highly inconvenient for judges, because in the event that they needed to do a deck check (which would require them to inspect each card in the deck and compare it against the deck list the player provided, which in this case was several pages long), it would, again, take a very long time.
** Maik would go on to be an even more influential judge, authoring some of the clarifications and rulings that addressed key holes in the game. Some of these rules are used to this day.

* The unusual "[[https://yugipedia.com/wiki/Yu-Jo_Friendship Yu-Jo Friendship]]" involves physical interaction with your opponent, and it has synergy with "[[https://yugipedia.com/wiki/Unity Unity]]" to force the opponent to accept the handshake. A story about a player using this to force their opponent to shake a filthy hand led to rulings that allow the opponent to simply say "I accept your handshake" to fulfill this card's requirements.

* The worst examples of this in Yu-Gi-Oh are Yata-Garasu and the two Envoys. All of the other cards on the Forbidden list are pivotal in combos. These three cards were banned just because they were ''[[GameBreaker that broken.]]'' Not helping the Envoys' case is a rule known as priority, which allows the player to activate their effects (which can normally only be activated at times when the player could activate a Normal Spell) immediately when they're Summoned, before the opponent has the chance to activate cards that would destroy them. Following the introduction of the Xyz monsters in the game, the OCG and TCG had their priority rulings patched to prevent people from calling priority on Ignition monster effects. Black Luster Soldier - Envoy of the Beginning has since been taken off the list. Chaos Emperor Dragon required errata to undo its banning: the player cannot activate any other card effects on the turn its nuke is used, and the damage is only done with respect to the opponent's cards that are sent to the Graveyard. Of the three cards, only Yata remained banned for a long time (The latest banlist made it Limited). [[note]]Yata-Garasu was a 200 ATK spirit monster that made the opponent skip their next draw phase whenever it connected. Because it bounced itself at the end of turn, it was effectively immune everything other than Quick-Play and Trap cards, so if it got through, and you didn't have an answer that very second, you almost certainly lost the game. and you have to sit there and take 200 damage each turn and hope he milled out before he killed you. [[/note]]

* In ''VideoGame/YuGiOhMasterDuel'', one of the first event hosted in the game was an [=Xyz=] festival that forced players to use only [=Xyz=] monsters, banning not just non-Xyz Extra deck monsters but also archetypes that don't revolve around Extra deck plays such as Eldlich and Monarchs to prevent players from cheesing the event. To encourage players to participate in the event, players are awarded Gems even if they lost the duel (100 for winning & 50 for losing and none at all if they surrender). However, players soon found out that it was far more efficient to lose twice in quick succession than to play a legitimate game that could last up to 15 minutes, thus this caused most of them to run self-burn decks that was designed to quickly deplete their own LP as fast as possible in order to attain gems as efficiently as possible, with only little investment required compared to the cost of building a competent [=Xyz=] deck. As a result, Konami increased the reward for winning from 100 to 500 in order to incentivize legitimate [=Xyz=] duels. Subsequent events such as [=N/R=] and Synchro Festivals flat-out bans any cards that purposely deplete your LP as fast as possible while still keeping the greater reward for winning in order to deter any further self-burn decks in the events.

* With the release of Xyz Monsters, there was a brief period where there were very few written rules about how they actually work - one key problem was the fact that the monster used for Xyz Summoning stayed on the field until "detached" by an effect. Fine, but when do effects that specify when a monster "leaves the field" trigger? WordOfGod said that they trigger on Xyz Materials being detached, and ''all hell broke loose''. Two already powerful cards got so absurdly broken that a single copy could easily fetch well over 100 dollars. Konami quickly made a rule change: Xyz Materials being detached ''never'' trigger such effects, because they aren't treated as cards anymore. It's just as weird as it sounds.
** These two cards were "Sangan" and "Tour Guide from the Underworld", along with any given Rank 3 (at the time, Number 17 Leviathan Dragon was favored). The combo is this: Tour Guide is summoned, whose effect summons a level 3 Fiend-type monster from the Deck, at the cost of negating that monster's effect. This monster would be Sangan. They overlay to form Number 17, whose effect is to "detach" a card to become stronger. The effect negation of Tour Guide is now void, since Sangan's state has changed. Number 17 detaches Sangan to become stronger, and Sangan's effect activates: when it is sent from the field to the graveyard, it adds a 1500-ATK-or-less monster from the Deck to the hand, such as another Tour Guide. So, to summarise, at no loss of hand advantage (a very important resource in Yu-Gi-Oh), you have a 2500 ATK beatstick facing your opponent down. This is no longer possible due to the new ruling. That said, cards that activate when "sent to the graveyard" will still activate - just not the ones that require being sent from the field to the graveyard.