Respite

The Fog effect is old and squarely in green's wheelhouse; stapling lifegain to it is what reframes the trick from pure defense into a tempo swing. The more attackers your opponent commits, the more you bank for surviving them, and that scaling is the whole design idea. A naked Fog tells the aggressor to attack again next turn; this one tells them that every creature they sent in just refilled the wall they were trying to break. The instant speed matters more than the rate suggests, because it lets you hold up the answer through the declare-attackers step and decide whether the life is worth a card only after the board has committed. Green is the color that gets to undo a combat step outright, and Respite is one of the early experiments in what that prevention should cost: it sits dead until creatures are swinging, it does nothing to the board, and it spends a card to buy a turn you may or may not need. The lifegain rider is the sweetener that makes a purely reactive blank worth running, paying out in proportion to how badly you needed it. That payout-scales-with-the-threat structure is the reusable idea, and it has shown up in green damage prevention since.