Defenestrate

The clause that pays for this card is the exemption: a three-mana instant that kills almost anything, so long as it can't fly. Black's clean unconditional removal has always come at a premium (Murder priced destruction at the same slot with no strings), so the design here trades one small blind spot for a slightly friendlier cost profile. That blind spot is doing real work: fliers are the creatures black most wants to answer and least wants to block, and this spell politely declines to touch them. What's left is a piece of ground-control removal, an instant that snaps up the beefy attacker or the mana-hungry midrange threat but leaves the evasive finishers for something else. Black kill spells have long been built around a single carve-out (Doom Blade skipping black, Ultimate Price hitting only monocolored things, Go for the Throat sparing artifacts), each one a different answer to the question of how to make efficient removal cost less without making it universal. The flavor of the name is the whole gag: you are throwing the target out a window, which is a fate you cannot inflict on anything already airborne. It is a small, honest joke wrapped around a small, honest restriction, and both the pun and the design point at the same seam in the card.