Unrooted Ancestor

A 3/2 with flash that eats one of your own creatures to become indestructible until end of turn: the fodder here buys durability, not card advantage or drain, which sets it apart from the sacrifice outlets black usually builds around. The self-tap is the clause doing the balancing. Activating it taps the Ancestor, so a body spent as a shield on your opponent's turn cannot sit back to block the next attacker; without that line, an on-demand indestructible flash creature would blank most combat math and a chunk of targeted removal for a single mana. Flash lets it hold up that mana and ambush an attacker, cashing in a spent token or a creature already walking to the graveyard to trade up while surviving. The survivor is always the Ancestor itself, not the creature it consumes: you feed it your weakest body to carry the 3/2 through a sweeper or a burn spell aimed at it. It sits in a long black lineage of creatures that convert other creatures into resources, feeding the sacrifice-and-recur loops mono-black and aristocrat shells have run for years, but it narrows that idea to a single purpose. The thing it protects is on the battlefield, and the thing it spends was already expendable.