Sacrifice

The original ritual-by-cannibalism. Where Dark Ritual fixed the conversion rate at three mana for one, this version makes the math conditional on what you are willing to give up: feed it a creature, and you get its mana value back in black mana at instant speed. The design space that opens is the entire history of black's sacrifice-for-mana subtheme. Strategically it is a one-shot accelerant, not an engine: a single creature in, a burst of mana out, with no creature-type restriction and no ceiling beyond what you can put into play. That makes it a combo piece in any shell that can land a large-mana-value body cheaply (a reanimated fatty, a creature cheated into play that you no longer need on the board) and a desperation tool in fair decks that need to turn one expensive creature into the mana for a spell that matters more. The friction Wizards has used to balance the descendants of this idea (capping the mana produced, restricting the creature, requiring a death trigger and a permanent that taps instead of a free instant) is simply absent here. The cost is the creature, and the payoff scales with that creature's mana value regardless of what it cost to put on the battlefield, which is exactly the reason cheated-in fatties make the math break. Black has spent thirty years iterating on this premise without ever quite reprinting it: capped, gated, or geared down, but never again this open.