Gnaw to the Bone is a common Instant card from Innistrad (ISD), collector number 183. Current market price: $0.30 (foil $11.59), TCGplayer market prices via Scryfall.
You gain 2 life for each creature card in your graveyard. Flashback {2}{G} (You may cast this card from your graveyard for its flashback cost. Then exile it.)