Final Flourish is a common Instant card from March of the Machine (MOM), collector number 104. Current market price: $0.17 (foil $0.19), TCGplayer market prices via Scryfall.
Kicker—Sacrifice an artifact or creature. (You may sacrifice an artifact or creature in addition to any other costs as you cast this spell.) Target creature gets -2/-2 until end of turn. If this spell was kicked, that creature gets -6/-6 until end of turn instead.