Isshin, Two Heavens as One
Legendary Creature — Human Samurai
If a creature attacking causes a triggered ability of a permanent you control to trigger, that ability triggers an additional time.
Trained by the Imperials but disillusioned by their rigidity, he gave his heart—and his swords—to the Asari Uprising.
Illustrated by
Kamigawa: Neon Dynasty#224RareEnglishLegality
Rulings
Isshin, Two Heavens as One's ability affects only triggered abilities with conditions that are directly related to attacking, such as “whenever [this creature] attacks” or “whenever you attack with one or more creatures.” It does not affect triggered abilities with other trigger conditions, such as “whenever [this creature] becomes tapped.”
Isshin's effect doesn't copy the triggered ability; it just causes the ability to trigger twice. Any choices made as you put the ability onto the stack, such as modes and targets, are made separately for each instance of the ability. Any choices made on resolution are also made individually.