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is the symbol for infinity, which has been used in a few exceptionally rare cases in the anime and manga as a monster's ATK or DEF value.

Strictly speaking, ∞ is not actually a number, but rather the concept of a value greater than any number. A monster with ∞ ATK cannot be destroyed by battle unless it battles another monster that also has ∞ ATK (and both are in Attack Position), in which case the two would destroy each other in a Double KO. If a monster with ∞ ATK attacked another Attack Position monster with non-infinite ATK, the controller of the latter would take an infinite amount of battle damage, instantly dropping their Life Points to 0.



  • At one point when the five pieces of "Exodia" were gathered, the complete "Exodia" was shown as a monster with an ATK of ∞, representing "Exodia's" automatic victory condition.
  • In Yu-Gi-Oh! R - Duel Round 042, Dark Yugi used the effect of "Obelisk the Tormentor" to increase its ATK to ∞. However, his opponent, Yako Tenma, controlled "The Wicked Avatar", whose effect would make its own ATK and DEF equal to that of the strongest monster on the field + 1. This caused the ATK and DEF of "The Wicked Avatar" to become ∞ as well. True to actual math, the two ATK values were treated as equal to each other (∞ + 1 = ∞ and is not greater than ∞); shortly after, with the aid of "Divine Evolution", the two monsters were able to destroy each other in battle in a Double KO.


  • No monster with ∞ ATK or DEF has ever been seen in Defense Position.
  • There has not yet been an instance in the anime or manga where a player has achieved an infinite number of Life Points, although it would be theoretically possible by simply activating a card such as "Mystik Wok" on a monster with ∞ ATK or DEF.
    • It is unclear what would happen if a player with ∞ Life Points were to take ∞ damage (by a direct attack or otherwise), as ∞ subtracted from itself is an indeterminate value (for example, any number would be correct, as any number can be added to ∞ to yield ∞).
  • Technically speaking, Yami Yugi's maneuver with "Legendary Knight Hermos" would have yielded an ATK greater than ∞, if ∞ has its usual meaning of the smallest possible infinity. In math, it can be proven that adding or multiplying ∞ by any number (even multiplying ∞ by itself) yields a value equal to ∞, but multiplying a number (in this case, 2800) by another number (in this case, 3) an infinite number of times yields a value strictly greater than ∞. However, this subtlety is not properly picked up on in the anime, as Yami Yugi states that the ATK of "Legendary Knight Hermos" is ∞, and "Timaeus the Knight of Destiny" is destroyed by battle.
    • Presumably, a maneuver like this would be the only way to destroy a Defense Position monster with ∞ DEF by battle, by getting a monster whose ATK is higher than that DEF.