Warrened Doll

Warrened Doll cannot be sacrificed while it is a creature.
At the beginning of your end step, if Warrened Doll
is on the battlefield, you lose 1 life. If it is in your graveyard, return it to the battlefield tapped.
{1}, {t}: Untap Warrened Doll. It becomes a 3/1 artifact creature with haste and hexproof until end
of turn.
{p/b}: Sacrifice Warrened Doll.

"Its heart never beats—but it never stops."