If an ability says "target creature," does the creature have to be on the battlefield? I think I found a loophole that depends on the answer.
Yes, it does. The rules say:
109.2. If a spell or ability uses a description of an object that includes a card type or subtype, but doesn’t include the word “card,” “spell,” “source,” or “scheme,” it means a permanent of that card type or subtype on the battlefield.
i.e., "creature" can only mean a creature permanent on the battlefield.