Hidden Horror
Creature — Horror
When this creature enters, sacrifice it unless you discard a creature card.
Clint Langley
Classic Sixth Edition (6ED)
• #137Rulings
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.
(wotc • 2008-04-01)
If the creature is no longer on the battlefield when the ability resolves, you may still perform the action if you want.
(wotc • 2008-04-01)
Rulings
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.
(wotc • 2008-04-01)
If the creature is no longer on the battlefield when the ability resolves, you may still perform the action if you want.
(wotc • 2008-04-01)