∞ 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.