Brightwake Watcher

Trample
{t}: Add {r} or {g} to your mana pool. If this mana is used to cast a Horror creature spell this turn, put a +1/+1 counter on Brightwake Watcher.
Whenever Brightwake Watcher deals combat damage to a player, exile the top card of your library. If it's converted mana cost is 4 or less, you may play that card this turn.