Slugahead

Devolve (Whenever a creature enters the battlefield, if its power or toughness is less than this creature's, put a -1/-1 counter on this.)
{1}: Look at the top eight cards of your library. You may reveal a card with converted mana cost equal to Slugahead's toughness. If you do, exile it face down. Any player may activate.
Whenever Slugahead dies, each player puts all face down cards they own in their hand.