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| − | [[File:Infinite loop.gif|thumb|The famous infinite loop that allowed [[Yugi Muto]] to defeat "[[Slifer the Sky Dragon ( | + | [[File:Infinite loop.gif|thumb|right|200px|The famous infinite loop that allowed [[Yugi Muto|Yugi]] to defeat "[[Slifer the Sky Dragon (original)|Slifer the Sky Dragon]]"]] |
An '''infinite loop''' is a never-ending cycle of effects [[Activate|activating]] in [[Respond|response]] to each other, or a series of [[Continuous Effect]](s) that never settle. | An '''infinite loop''' is a never-ending cycle of effects [[Activate|activating]] in [[Respond|response]] to each other, or a series of [[Continuous Effect]](s) that never settle. | ||
| − | There are two distinct types of infinite loops: loops with no net change and loops with net change. | + | There are two distinct types of infinite loops: loops with no net change and loops with net change. There are also ''controlled loops'', which are similar to infinite loops but are instead created by a player intentionally repeating a set of actions or making the same decisions rather than game mechanics. |
==Loops with no net change== | ==Loops with no net change== | ||
| − | These occur when a series of mandatory actions repeat after each other in a cycle, and there is no net change after each cycle, such that the game state is identical at the beginning and end of any cycle. | + | These occur when a series of mandatory actions repeat after each other in a cycle, and there is no net change after each cycle, such that the game state is identical at the beginning and end of any cycle. |
| − | + | These types of infinite loops are illegal in gameplay, meaning that a player may not voluntarily [[activate]] any card if its activation would cause such a loop. If such a loop is caused by something involuntary, such as a player conducting their [[normal draw]] or a mandatory effect, then the card ruled to be the source of the infinite loop is automatically destroyed by game mechanics. | |
===Pole Position=== | ===Pole Position=== | ||
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"[[Pole Position]]", "[[Luminous Spark]]", and "[[Gemini Elf]]" (1900 ATK) are face-up on the field. | "[[Pole Position]]", "[[Luminous Spark]]", and "[[Gemini Elf]]" (1900 ATK) are face-up on the field. | ||
| − | If a player | + | If a player attempts to Summon "[[X-Head Cannon]]", the following would occur: |
* "X-Head Cannon" would be Summoned with 1800 ATK. | * "X-Head Cannon" would be Summoned with 1800 ATK. | ||
* Since "X-Head Cannon" is a [[LIGHT]] monster, "Luminous Spark" increases its ATK by 500, to 2300. | * Since "X-Head Cannon" is a [[LIGHT]] monster, "Luminous Spark" increases its ATK by 500, to 2300. | ||
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* The above sequence would repeat infinitely, with the ATK of "X-Head Cannon" never settling. | * The above sequence would repeat infinitely, with the ATK of "X-Head Cannon" never settling. | ||
| − | + | Therefore, it is an illegal move for either player to Summon "X-Head Cannon".<ref name="UDE P-R">[http://web.archive.org/web/20090220140220/http://entertainment.upperdeck.com/yugioh/en/gameplay/faqs/cardfaqs/default.aspx?first=P&last=R UDE FAQ]: Individual Card Rulings [P-R]</ref> | |
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====Involuntary==== | ====Involuntary==== | ||
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* The above sequence would repeat infinitely, with the ATK of "Muka Muka" never settling. | * The above sequence would repeat infinitely, with the ATK of "Muka Muka" never settling. | ||
| − | + | Since this loop was caused by a mandatory action, it cannot be prevented by restricting the player's actions. Since the loop cannot be avoided, "[[Pole Position]]" will be [[destroy]]ed by [[game mechanics]].<ref name="UDE P-R"/> | |
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===Amplifier=== | ===Amplifier=== | ||
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Player 1 [[control]]s a "[[Jinzo]]" which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". "Jinzo" is equipped with "[[Amplifier]]". | Player 1 [[control]]s a "[[Jinzo]]" which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". "Jinzo" is equipped with "[[Amplifier]]". | ||
| − | If Player 1 | + | If Player 1 attempts to activate "[[Imperial Order]]", the following would occur: |
* "Imperial Order" negates the effect of "Snatch Steal" ("Amplifier" cannot be negated). | * "Imperial Order" negates the effect of "Snatch Steal" ("Amplifier" cannot be negated). | ||
* Since "Snatch Steal" is now negated, control of "Jinzo" returns to its owner Player 2. | * Since "Snatch Steal" is now negated, control of "Jinzo" returns to its owner Player 2. | ||
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* The above sequence would repeat infinitely, with the player who controls "Jinzo" never settling. | * The above sequence would repeat infinitely, with the player who controls "Jinzo" never settling. | ||
| − | + | Therefore, it is an illegal move for Player 1 to activate "Imperial Order".<ref name="UDE A-C">[http://web.archive.org/web/20090217182013/http://entertainment.upperdeck.com/yugioh/en/gameplay/faqs/cardfaqs/default.aspx?first=A&last=C UDE FAQ]: Individual Card Rulings [A-C]</ref> | |
| − | + | If Player 1 had already controlled "Imperial Order" before activating "Snatch Steal", then Player 1 activating "Snatch Steal" targeting "Jinzo" (equipped with "Amplifier") would be an illegal move. | |
=====Involuntary===== | =====Involuntary===== | ||
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* The above sequence would repeat infinitely, with the player who controls "Jinzo" never settling. | * The above sequence would repeat infinitely, with the player who controls "Jinzo" never settling. | ||
| − | + | Since this loop was caused by a mandatory effect, it cannot be prevented by restricting the player's actions. Since the loop cannot be avoided, whichever card is identified as the cause will be [[destroy]]ed by [[game mechanics]] (no official ruling has been issued as to which is the cause). | |
====Negation==== | ====Negation==== | ||
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* The above sequence would repeat infinitely, with which effect is active never settling. | * The above sequence would repeat infinitely, with which effect is active never settling. | ||
| − | + | Therefore, it is an illegal move for Player 1 to activate "Royal Decree".<ref name="UDE A-C"/> | |
| − | + | If Player 2 had already controlled "Royal Decree" before Player 1 activated "Skill Drain", then Player 1 activating "Skill Drain" would be an illegal move. | |
=====Involuntary===== | =====Involuntary===== | ||
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* The above sequence would repeat infinitely, with which effect is active never settling. | * The above sequence would repeat infinitely, with which effect is active never settling. | ||
| − | ' | + | Since this loop was caused by a mandatory effect, it cannot be prevented by restricting the player's actions. Since the loop cannot be avoided, whichever card is identified as the cause will be [[destroy]]ed by [[game mechanics]] (no official ruling has been issued as to which is the cause). |
===Cyber Blader=== | ===Cyber Blader=== | ||
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====Voluntary==== | ====Voluntary==== | ||
Player 1 [[control]]s three monsters, one of which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". | Player 1 [[control]]s three monsters, one of which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". | ||
| − | + | If Player 2 attempts to Summon "[[Cyber Blader]]", the following would occur: | |
| − | * Since Player 1 controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The | + | * Since Player 1 controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The 'stolen' monster returns to Player 2's control. |
| − | * Since Player 1 now controls two monsters, the effect of "Cyber Blader" instead doubles its ATK. The effect of "Snatch Steal" is no longer negated, so Player 1 gains control of the | + | * Since Player 1 now controls two monsters, the effect of "Cyber Blader" instead doubles its ATK. The effect of "Snatch Steal" is no longer negated, so Player 1 gains control of the 'stolen' monster. |
| − | * Since Player 1 now controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The | + | * Since Player 1 now controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The 'stolen' monster returns to Player 2's control. |
* The above sequence would repeat infinitely, with the player who controls the monster equipped with "Snatch Steal" never settling. | * The above sequence would repeat infinitely, with the player who controls the monster equipped with "Snatch Steal" never settling. | ||
| − | + | Therefore, it is an illegal move for Player 2 to Summon "Cyber Blader". | |
| − | + | If Player 2 had already controlled "Cyber Blader" before Player 1 activated "Snatch Steal", then Player 1 activating "Snatch Steal" (targeting a monster other than "Cyber Blader") would be an illegal move. | |
====Involuntary==== | ====Involuntary==== | ||
Player 1 [[control]]s two monsters, one of which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". Player 1 also controls "[[Jam Breeding Machine]]". Player 2 controls "Cyber Blader". | Player 1 [[control]]s two monsters, one of which is [[owner|owned]] by Player 2, but being controlled by Player 1 due to "[[Snatch Steal]]". Player 1 also controls "[[Jam Breeding Machine]]". Player 2 controls "Cyber Blader". | ||
| − | + | During Player 1's [[Standby Phase]], the following would occur: | |
| − | * | + | * "Jam Breeding Machine's" mandatory effect Summons a "[[Slime Token]]" to Player 1's field. |
| − | * Since Player 1 controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The | + | * Since Player 1 controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The 'stolen' monster returns to Player 2's control. |
| − | * Since Player 1 now controls two monsters, the effect of "Cyber Blader" instead doubles its ATK. The effect of "Snatch Steal" is no longer negated, so Player 1 gains control of the | + | * Since Player 1 now controls two monsters, the effect of "Cyber Blader" instead doubles its ATK. The effect of "Snatch Steal" effect is no longer negated, so Player 1 gains control of the 'stolen' monster. |
| − | * Since Player 1 now controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The | + | * Since Player 1 now controls three monsters, the effect of "Cyber Blader" negates the effect of "Snatch Steal". The 'stolen' monster returns to Player 2's control. |
* The above sequence would repeat infinitely, with the player who controls the monster equipped with "Snatch Steal" never settling. | * The above sequence would repeat infinitely, with the player who controls the monster equipped with "Snatch Steal" never settling. | ||
| − | ' | + | Since this loop was caused by a mandatory effect, it cannot be prevented by restricting the player's actions. Since the loop cannot be avoided, whichever card is identified as the cause will be [[destroy]]ed by [[game mechanics]] (no official ruling has been issued, but it will likely be either "[[Snatch Steal]]" or "[[Cyber Blader]]"). |
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==Loops with net change== | ==Loops with net change== | ||
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* The effect of "Hiro's Shadow Scout" will again make the opponent draw 3 cards. | * The effect of "Hiro's Shadow Scout" will again make the opponent draw 3 cards. | ||
* "Morphing Jar #2" will continue to return the two monsters to the Deck and reset them face-down onto the field, where "All-Out Attacks" will flip them. | * "Morphing Jar #2" will continue to return the two monsters to the Deck and reset them face-down onto the field, where "All-Out Attacks" will flip them. | ||
| − | * This infinite loop repeats until Player 2 has drawn close to their whole Deck, at which point the effect of "Hiro's Shadow Scout" will force Player 2 to draw when they do not have enough cards in their Deck. This will cause Player 2 to lose the Duel due to a | + | * This infinite loop repeats until Player 2 has drawn close to their whole Deck, at which point the effect of "Hiro's Shadow Scout" will force Player 2 to draw when they do not have enough cards in their Deck. This will cause Player 2 to lose the Duel due to a Deck out. |
====End with no net change==== | ====End with no net change==== | ||
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* This infinite loop repeats until Player 2 has milled their whole Deck, at which point the effect of "Needle Worm" ceases to cause the opponent to mill any cards. The loop now has no net change. | * This infinite loop repeats until Player 2 has milled their whole Deck, at which point the effect of "Needle Worm" ceases to cause the opponent to mill any cards. The loop now has no net change. | ||
| − | At this point, just as with infinite loops with no net change, the card that began the loop, "All-Out Attacks", would be | + | At this point, just as with infinite loops with no net change, the card that began the loop, "All-Out Attacks", would be destroyed by game mechanics. Once Player 1 ends their turn, Player 2 will be unable to draw a card during their Draw Phase and will lose the Duel. |
===Red-Eyes Flare Metal Dragon=== | ===Red-Eyes Flare Metal Dragon=== | ||
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This ruling can also be extrapolated to cover "Destiny HERO - Departed" with a nonzero ATK of 2000 or less while the player controls "[[Slifer the Sky Dragon]]". | This ruling can also be extrapolated to cover "Destiny HERO - Departed" with a nonzero ATK of 2000 or less while the player controls "[[Slifer the Sky Dragon]]". | ||
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| + | ===Light and Darkness Dragon=== | ||
| + | The negation effect of "[[Light and Darkness Dragon]]" will only activate once while the effect of "[[Reverse Trap]]" is applying.<ref name="UDE L-O">[http://web.archive.org/web/20090220023927/http://entertainment.upperdeck.com/yugioh/en/gameplay/faqs/cardfaqs/default.aspx?first=L&last=O UDE FAQ]: Individual Card Rulings [L-O]</ref> In addition to preventing abuse, this also prevents infinite loops. | ||
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| + | If this ruling were not in place, infinite loops would occur with many mandatory Trigger Effects. For example, the following would happen during the opponent's [[End Phase]] if that player controls "[[Judgment Dragon]]": | ||
| + | * The [[mandatory effect]] of "Judgment Dragon" activates to send cards from the Deck to the Graveyard. | ||
| + | * The mandatory effect of "Light and Darkness Dragon" is Chained, negating the effect of "Judgment Dragon" and increasing its own ATK and DEF by 500. | ||
| + | * The mandatory effect of "Judgment Dragon" activates to send cards from the Deck to the Graveyard. | ||
| + | * The mandatory effect of "Light and Darkness Dragon" is Chained, negating the effect of "Judgment Dragon" and increasing its own ATK and DEF by 500. | ||
| + | * The above sequence would repeat infinitely. | ||
==In the anime== | ==In the anime== | ||
| − | + | Infinite loops with net change have been seen a number of times in the anime: | |
| + | |||
| + | * In [[Yu-Gi-Oh! - Episode 067|episode 67]] of ''Yu-Gi-Oh!'', [[Yami Yugi]] used the effects of [[Strings]]' "[[Slifer the Sky Dragon]]", "[[Revival Jam]]", and "[[Card of Safe Return]]" against him by taking control of "[[Revival Jam]]" by "[[Brain Control]]", forcing "Slifer" to attack and destroy "Revival Jam" over and over. This caused "Card of Safe Return" to make Strings continuously draw from his Deck until he Decked out and lost the Duel. This is arguably the most famous infinite loop to be seen in the anime. | ||
| + | * In [[Yu-Gi-Oh! - Episode 182|episode 182]] of ''Yu-Gi-Oh!'', Yami Yugi used the effects of "[[Legendary Knight Critias]]" (which had absorbed the effect of "[[Attack Guidance Barrier]]") and "[[Legendary Knight Hermos]]" to continuously redirect attacks between them while another effect of "Hermos" increased its ATK each time. By anime mechanics, this caused the ATK of "Hermos" to become [[∞]]. | ||
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| + | ==Controlled loops== | ||
| + | These are not infinite loops, but rather a series of voluntary actions that can be repeated as many times as a player wants. There is no uncontrollable element to these loops and a player can choose to stop them at any time, so they are legal to use. | ||
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| + | Some loops that require only a few cards (fewer than 4) to pull off have caused cards to become [[Forbidden]] or [[Limited]] on the current Forbidden/Limited lists, as otherwise their presence would be detrimental to gameplay. | ||
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| + | ===Quillbolt Loop=== | ||
| + | {{main|Quillbolt Loop}} | ||
| + | This uses the effect "[[Quillbolt Hedgehog]]" to [[Special Summon]] itself by having a [[Tuner monster|Tuner]] on the field along with a monster effect that Tributes a monster for damage such as "[[Cannon Soldier]]". "Quillbolt" can be Tributed again and again and continuously revived, as long as "[[Imperial Iron Wall]]" prevents "Quillbolt Hedgehog" from being [[banish]]ed by its own effect. | ||
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| + | A far more consistent variation of this loop uses "[[Plaguespreader Zombie]]". Summon both "Quillbolt" and "Plaguespreader" to the field, and Xyz Summon "[[Ghostrick Socuteboss]]", then activate its effect. Then, Summon "[[Ghostrick Dorklord]]" by using "Socuteboss as the Xyz Material", then detach an Xyz Material (not "Socuteboss)" to add a generic "Ghostrick" Spell/Trap to your hand. Place this Spell/Trap back on top of your Deck to revive "Plaguespreader", then revive "Quillbolt" with its effect. This returns to the start of the loop. | ||
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| + | ===Flint Lock Loop=== | ||
| + | {{main|Flint Lock Loop}} | ||
| + | This uses "[[Flint]]" and two "[[Flint Lock]]s" to pass the "Flint" back and forth. The [[Spell Card]] "[[Morale Boost]]" is used to gain 1000 [[Life Points]] every time an [[Equip Card]] is equipped. Because no Equip Card leaves the field, the effect to lose 1000 Life Point is never reached. This allows a player to gain an unlimited number of Life Points while the opponent may be powerless to stop it. | ||
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| + | ===Gearfried Loop=== | ||
| + | If a player controls "[[Gearfried the Iron Knight]]", then it is possible to activate "[[Butterfly Dagger - Elma]]" an unlimited number of times per turn, by [[equip]]ping it to "Gearfried", whose effect will [[destroy]] it, at which point "Elma's" effect will return it to the hand to be equipped again. This can easily be combined with "[[Royal Magical Library]]" to draw an unlimited number of cards in one turn (causing an easy [[Exodia]] [[FTK]], etc.). Another option is to combine it with "[[Spell Absorption]]" to gain an arbitrarily high number of [[Life Points]]; adding "[[Fire Princess]]" gives an unlimited amount of damage to inflict in one turn on top of that. This loop is the reason why "Butterfly Dagger - Elma" is currently [[Forbidden]] on the Forbidden/Limited List. | ||
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| + | ===Gate Material Loop=== | ||
| + | By combining "[[Fusion Gate]]" and "[[Chain Material]]", it is possible to Summon or activate nearly any card an unlimited number of times per turn, through the correct (and very risky) setup. These loops generally revolve around Fusion Summoning several [[Fusion Monster]]s by [[banish]]ing [[Fusion Material Monster]]s from the [[Main Deck]], followed by using said monsters to activate effects or Summon other monsters, then finally Fusion Summoning "[[Elemental HERO Electrum]]" to return the originally banished monsters back to the Deck to be banished again. For an example, see [[Elemental HERO Gustav Max OTK]], an [[OTK]] that involves Summoning "[[Superdreadnought Rail Cannon Gustav Max]]" at least four times in one turn. For further and more detailed examples of possible setups, see [http://forum.duelingnetwork.com/index.php?/topic/99712-gate-material-decks-the-ultimate-comprehensive-guide/#entry1652884 this external link]. | ||
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| + | ===Primal Seed Loop=== | ||
| + | If a card is active that banishes Spell Cards that would go to the Graveyard (such as "[[Macro Cosmos]]" or "[[Banisher of the Light]]"), and there is a "[[Black Luster Soldier - Envoy of the Beginning]]" or "[[Chaos Emperor Dragon - Envoy of the End]]" on the field, then any player with two copies of "[[Primal Seed]]" and a [[Normal Spell Card|Normal]] or [[Quick-Play Spell Card]] in their hand can activate that Spell Card an unlimited number of times per turn, by repeatedly using one copy of "Primal Seed" to bring back the other copy along with that Spell Card. This allows for an [[OTK]] with a card as weak as "[[Sparks]]", as well as numerous other possibilities such as arbitrarily high Life Points or ATK. This loop is why "Primal Seed" is currently [[Limited]] in the ''OCG''; it was Limited in the ''TCG'' as well until [[April 2014 Lists (TCG)|1 April 2014]]. | ||
| − | + | ===Wicked Worm Beast Loop=== | |
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| − | + | If [[Wicked Worm Beast]] is special summoned in the [[End Phase]] of the turn it is automatically returned to the hand. Therefore, if a player has 7 or more cards in their hand in the End Phase of the turn and [[Dark World Grimoire]] active, they can discard Wicked Worm Beast, Special Summon it with Grimoire, and return it to the hand again. Although this has limited value, if the opponent activated [[Maxx "C"]], they could deck out. Similar strategies can occur using [[DNA Surgery]] and [[Cyber Summon Blaster]] or [[Soul-Absorbing Bone Tower]], the latter of which works with [[Zombie World]]. This loop is more easily achieved using [[Silent Wobbe]] with a card that takes control of it. | |
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| − | * In [[Yu-Gi-Oh! | + | ===In the anime=== |
| + | * In [[Yu-Gi-Oh! GX - Episode 064|episode 64]] of ''Yu-Gi-Oh! GX'', [[Syrus]] used the mandatory effect of [[Hassleberry]]'s "[[Ultimate Tyranno]]" against him, forcing it to attack and destroy "[[Decoyroid]]" over and over while the combined effects of "[[Ambulanceroid]]" and "[[Rescueroid]]" continuously Summoned it back to the field. This allowed Syrus's "[[Cyber Summon Blaster]]" to continuously damage Hassleberry until he lost the Duel. | ||
| + | * In [[Yu-Gi-Oh! ZEXAL - Episode 098|episode 98]] of ''Yu-Gi-Oh! ZEXAL'', [[Yuma Tsukumo]] and [[Astral]] fused into [[Dark ZEXAL]] against [[Vector]], with the latter, who was blinded by rage, taking control. He equipped "[[DZW - Chimera Clad (anime)|Dark ZEXAL Weapon - Chimera Clad]]" to "[[Number C39: Utopia Ray V (anime)|Chaos Number 39: Utopia Ray V]]", granting it immunity by battle destruction and the ability to [[attack]] once again with doubled [[ATK]] whenever Dark ZEXAL took [[battle damage]] from attacks involving it. He then proceed to attack the higher-ATK "[[Number 104: Masquerade (anime)|Number 104: Masquerade]]", taking the first damage and triggering the first ATK boost. However, Vector [[activate]]d "[[Extra Hundred]]" in response to the second attack, so that "Masquerade" always had 100 more ATK than "Utopia Ray V". Astral didn't realize the danger, and continued to attack again and again, losing 100 [[LP]] each time, until he was down to 600. At that point, Yuma managed to cancel the fusion and promptly ended the turn, preventing the 500 damage of "[[Sargasso the Different Dimension Battlefield (anime)|Sargasso the Different Dimension Battlefield]]" from reducing their LP to 0. Had he not managed to, Astral would probably have continued the loop until he lost. | ||
==References== | ==References== | ||
