Thieving Rat King

Deathtouch
Whenever Thieving Rat King deals combat damage
to a player, that player exiles the top card of their
library. You may cast that card for free as long as it
remains exiled. If you cast a creature spell this way,
it becomes a Rat in addition to its other types.
"Everything belongs to the Rat King,
even the thoughts and dreams of others."