Angel's Grace

For one white mana, you buy an absolute guarantee: this turn you do not die, and your opponent does not win. Split second is what turns that promise into a wall. Once it is announced, players can't cast spells or activate non-mana abilities in response, so there is no fizzling it, no removing the source of your impending demise, no winning in reply. That uninterruptible window is precisely what makes it a combo enabler rather than a defensive trick. The two clauses do different jobs, and getting them confused is the classic mistake. The damage clause only props your life total at 1 against damage; it does nothing to life loss, sacrifice, or any other cost. The reason the famous Ad Nauseam line works is the other clause entirely: "you can't lose the game this turn." You draw your whole deck, your life total dives well into the negatives, and you simply do not lose, because state-based actions that would normally end you are switched off until the turn ends. Then you assemble lethal before that turn does. The "your opponents can't win" half is the closing argument: it seals the obvious escape of an opponent winning through some other condition while you are propped up. Note what it does not do: it protects nothing past end of turn and nothing on a future turn. That single-turn ceiling is what keeps a one-mana hard lock from being oppressive: the safety is total, the duration is fleeting, and you must do something with it before the turn closes.