Global Warming

Cumulative upkeep - a Snow permanent you control loses Snow for as long as Global Warming remains in play.

Whenever a creature an opponent controls is assigned to block, that creature’s controller loses 1 life.

At the end of combat, for each creature that blocked or was blocked this turn, its controller flips a coin; if they lose the flip, destroy that creature.

Once they discovered that humans taste good with marshmallows, this outcome was inevitable.