Skullcrack

Burn spells have always known how to handle creatures, sweepers, and counterspells; the matchup they historically could not solve was a life total racing out of range. Lifegain is the cleanest out an aggressive red deck faces, and a single resolved gain spell or lifelink swing erases a full turn of damage. This is the answer, and the design lives entirely in the riders. The three damage to a player or planeswalker is ordinary rate; what matters is that lifegain and damage prevention both shut off for the turn. The card does not stop an opponent from responding to it (anything on the stack can be answered, and an instant-speed gain spell cast in reply will resolve first), but it inverts the timing. The correct use is to hold it: let the opponent commit to stabilizing, then cast this in response. Their lifegain spell still resolves, but with the no-lifegain clause already in effect, the gain produces nothing while the three damage lands clean. The damage-prevention clause closes the other stabilizing route in the same motion, so a fog effect or any trick that works by preventing damage cannot save the turn either (a redirection effect that reroutes rather than prevents is a separate matter, and that one Skullcrack does not touch). Instant speed is the whole point. A sorcery-speed version would let the opponent simply gain life on their own turn and be done with it; at instant speed, the card waits for the moment of commitment and punishes it, the rare burn spell better held than cast on curve.