Hungry Troll Guide

{r}{g}: During combat after blockers have been assigned but before damage is dealt, reveal the
top card of your library. You may spend X mana,
where X is the revealed card's converted mana
cost (if it has no converted mana cost, X is considered spent). If you spent X, remove target creature you control from combat. If you did not
spend X, sacrifice Hungry Troll Guide. Shuffle
the revealed card back into your library.
"Tasty treats, what do we have here?"