Agonizing Demise is a common Instant card from Invasion (INV), collector number 92. Current market price: $0.18 (foil $1.54), TCGplayer market prices via Scryfall.
Kicker {1}{R} (You may pay an additional {1}{R} as you cast this spell.) Destroy target nonblack creature. It can't be regenerated. If this spell was kicked, Agonizing Demise deals damage equal to that creature's power to the creature's controller.