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.
Yes, when targeting a permanent, creature, artifact, enchantment, planeswalker or land, it must be on the battlefield. When targeting specifies targeting a spell, it must be on the stack (like with counterspell). There are exceptions to this, but they all specify how they work, for example:
- Animate Dead specifies it enchants a "creature card in a graveyard".
- Zombify uses the words "target creature from your graveyard" by saying it's coming from the graveyard, that's the only place it can be when you target it.
- Runic Repetion specifies it returns a card from exile, defining the zone where the card had to be to be targeted.