Time to Feed is a common Sorcery card from Duel Decks: Elspeth vs. Kiora (DDO), collector number 50. Current market price: $0.13, TCGplayer market prices via Scryfall.
Choose target creature an opponent controls. When that creature dies this turn, you gain 3 life. Target creature you control fights that creature. (Each deals damage equal to its power to the other.)