Pawn of Ulamog

Death and mana, welded into the same trigger. The body is incidental; what matters is that every nontoken creature you control turns its death into a 0/1 Spawn token, and each of those tokens converts back into one colorless mana on demand. That conversion rate is the whole engine: bodies become tokens, tokens become ramp, and a sacrifice-themed deck suddenly has a mana floor under its attrition. The token-exclusion clause is the discipline doing the balancing work: the Spawn it makes are themselves tokens, so they cannot feed the trigger, which stops the obvious loop of dying tokens spawning more tokens before they're even paid for. What's left is a payoff that scales with how much you're willing to feed into the graveyard, and it rewards a board built from real creatures rather than chaff. Black has plenty of cards that turn creature death into card draw, life drain, or counters; turning it into colorless mana is a rarer translation, and the colorless Eldrazi mana it produces points the engine toward exactly the kind of expensive payoffs that the rest of its tribe was built to cast. It is a quiet aristocrats piece whose reward is ramp rather than reach, and the deck that wants it is the deck already happy to watch its own creatures die.