Cinder Elemental

A 2/2 nobody plays for combat, parked on the board as a stored Fireball waiting for the right turn. The activated ability is the whole card: pay an X, tap, sacrifice the creature, and convert mana plus its own existence into uncapped damage at any target. The sacrifice clause is what lets that X-damage scale without a ceiling: it is a cost the design can afford to leave open precisely because the creature spends itself the instant it fires. This is one-shot artillery, not a repeatable engine, and the lack of any timing restriction is what makes it resilient. An opponent who points removal at the body does not defuse anything; they force a premature activation, since the controller can respond by sacrificing it in answer to the spell (assuming the mana is up and the summoning sickness has worn off). The real strategic axis is therefore mana, not survival: hold it while you build to a lethal X, and the only question is whether you have the lands to pull the trigger before you have to. Cash it early and you have traded a permanent for a small burn a dedicated spell delivers more cheaply. Its lineage runs through every creature that doubles as a deferred burn spell, the design that hands a creature deck a guaranteed late-game finisher or a way to burn down one stubborn creature at the moment of maximum leverage. For an opponent light on interaction, the loaded spell is unanswerable; only its mana can run dry.