Burn from Within

Most X-damage spells stop at the body count; this one closes the escape hatch on the way out. The recurring problem with scalable burn was always the creature that survives lethal damage anyway: the indestructible bruiser (a Theros god, anything animated by a Darksteel effect) that shrugs off however much you pay and stands there mocking you. Burn from Within folds two clauses into the damage event to answer that. First it strips indestructible for the turn, so the damage can actually be lethal against a creature that would otherwise laugh it off. Then, if that creature would die, it gets exiled rather than dying, which denies the graveyard recursion and death triggers a normal kill would hand back. The result is a single sorcery that doubles as flexible reach (point it at a face, a planeswalker, anything with a life total) and as a clean answer to the specific creatures damage-based removal cannot normally finish, provided you can afford the mana. The cost of that completeness is the cost every X-spell pays: it does nothing efficiently, scaling linearly with your available mana and asking you to overpay wherever a fixed-cost removal spell would simply do the job. It is removal that refuses to be cheap in exchange for refusing to be cheated.