原文The value of X is determined only as the undergrowth ability resolves. If the number of creature cards in your graveyard changes later in the turn, Kraul Harpooner is unaffected.
原文You choose the target of the triggered ability (or that it has no target) as it goes on the stack, but you choose whether the creatures fight as that ability resolves.
原文If you choose a target and the target creature is an illegal target when Kraul Harpooner's ability tries to resolve, the ability doesn't resolve and Kraul Harpooner doesn't get +X/+0. If the target creature is legal but Kraul Harpooner is no longer on the battlefield, the target creature won't deal or be dealt damage.