Xo, Maelstrom Murderess

Cascade (When you cast this spell, exile cards from
the top of your library until you exile a nonland card
that costs less. You may cast it without paying its
mana cost. Put the exiled cards on the bottom of your library in a random order.)
Whenever Xo, Maelstrom Murderess deals
combat damage to a player, it deals that much
damage to each creature that player controls.

There is death in the air tonight.