Bubbling Muck

Where Dark Ritual front-loads a fixed payoff from a single card, this distributes it across your board: every Swamp tapped after it resolves coughs up an extra black mana until the turn ends, so the spell's value is a function of land count rather than anything printed on the card itself. One Swamp tapped yields two black; five Swamps yield ten. It is the black equivalent of High Tide, a per-land multiplier that rewards going wide on Swamps and chaining the surplus into more lands, more rituals, and a payoff big enough to justify the turn. The trigger reads the Swamp subtype rather than basic status, so nonbasic Swamps (the original duals, the shocklands, any printed-Swamp land) feed the engine just as well as a basic does. What holds it in check is the same dependency working in reverse: it produces nothing off colored mana drawn from artifacts or from lands that are not Swamps, and the windfall expires when the turn does, pushing hard toward an explosive single-turn plan over any incremental gain. The design comes from an era that delighted in mana acceleration breaking the one-land-one-mana convention, the same sensibility behind the free spells and untap engines printed alongside it. Most rituals are one-shot fuel you spend and forget; this one opens a floodgate, then lets you pour through it with as many Swamps as the turn will allow.