Rain of Filth

Where Dark Ritual and Cabal Ritual spend a card to add a fixed lump of black, this one converts the board itself. Every land you control briefly gains a one-shot sacrifice ability that adds black, so the size of the burst is set by your land count, but the cost is the lands themselves: you spend them to fill the pool, and there is no replaying them this turn. The output is precise rather than arbitrary, scaling exactly with how committed you are to the all-in turn, and the surge is terminal. You mortgage the entire board into a single window of black mana, then end the turn diminished, with nothing to untap. That tradeoff is the whole design. It rewards a deck built to win on the spot, because the game has no second act once the lands are gone. The instant timing does real work beyond the obvious: because mana abilities don't use the stack, the conversion can be slipped into a response or held until the end of an opponent's turn to power an instant-speed payoff, rather than chaining the lands away inside your own main phase. A glass-cannon enabler in the strictest sense, where the resource being burned is not a card or a chunk of mana but the future of the game state, and the payoff has to clear a high bar: large enough to justify never untapping a land again.