Sidisi, Undead Vizier

Exploit found its perfect host here: a mechanic that asks you to feed a creature into the void in exchange for a reward, married to the single most valuable reward black has to offer. The body is almost beside the point, though a 4/6 with deathtouch trades up against most things and walls the rest. What matters is that exploiting a creature turns into Diabolic Tutor with legs, a Demonic Tutor that arrives stapled to a blocker and is willing to eat a sacrifice it was going to make anyway. Black's unrestricted tutoring has always been a deckbuilding luxury sold at a steep premium, usually paid in life or in a card from hand; here the cost is a creature you can choose to make worthless before you sacrifice it, a token, a creature with a death trigger, a thing that already did its job. The exploit clause is genuinely optional, so when there is nothing worth sacrificing the card simply lands as a sturdy beater, which keeps it from being dead weight in the games where you have no fodder. That flexibility is the whole pitch: a tutor effect that does not strand you when you draw it without a payload, attached to a permanent that demands an answer. It is the rare creature whose value comes entirely from what surrounds it, and the more a deck cares about sacrifice and search, the more it becomes a deterministic instruction rather than a fair card.