What is your favorite overlooked interaction piece?

I have been trying to make my decks more diversified and find cards that fit themes better, so I'm trying to find unique interaction pieces. I'm not talking [[Swords to Plowshares]], [[Vandalblast]] or [[Counterspell]]. What is your favorite pet / overlooked interaction piece?

Lately I have been running [[Ossification]] into more decks since most people don't run land destruction.