The Book of Exalted Deeds

Two abilities share this artifact, but the lifegain-into-Angels engine is scaffolding: a way to manufacture a target if you don't already have an Angel on the board. Everything hinges on the enlightened counter. Hand an Angel "You can't lose the game and your opponents can't win the game," and a wide swath of losing lines converts into permanent stalemates. Decking out no longer ends your game. Poison, commander damage, an opponent's own assembled win: all of it stops functioning. The same sentence disables opponents' alternate wins while leaving yours live, and that asymmetry separates a lifegain curiosity from an actual lock. The triple-white pip and the sorcery-speed, exile-yourself activation are the toll, and you pay it once for keeps: you spend the artifact permanently to install the counter, so you're buying a single key rather than a repeatable engine. The book's footprint comes less from constructed pedigree than from how it warps a table. A card that can render a game genuinely unlosable tends to get legislated against in casual playgroups, and it has become shorthand for the "can't lose the game / can't win the game" design axis that Wizards has periodically revisited. It is a lock printed as a lore artifact, and the flavor of a divine ledger granting the untouchable an unbeatable status lands exactly where the mechanics do.