Creature - Elephant 3/3, G (1) When Rogue Elephant enters the battlefield, sacrifice it unless you sacrifice a Forest.1 "When are the trees like grass?" -The One Thousand Questions
Illus. Steve White
4/1/2008: When the ability resolves, you choose whether to sacrifice the creature or perform the other action. If you can’t perform the other action, then you must sacrifice the creature.
4/1/2008: If the creature is no longer on the battlefield when the ability resolves, you may still perform the action if you want.