Martyrdom

Oracle Text

Until end of turn, target creature you control gains "0: The next 1 damage that would be dealt to target creature or player this turn is dealt to this creature instead." Only you may activate this ability.

Card Rulings

10/4/2004 If the target stops being a creature, you can’t redirect damage to it until/unless it becomes a creature again.
10/4/2004 If the target creature is not still on the battlefield when the damage is to be redirected, the damage stays where it is.
10/4/2004 Can be used to redirect damage from that creature to itself. This has no particularly useful effect.