Acidic Dagger is a rare Artifact card from Mirage (MIR), collector number 291. Current market price: $0.57, TCGplayer market prices via Scryfall.
{4}, {T}: Whenever target creature deals combat damage to a non-Wall creature this turn, destroy that non-Wall creature. When the targeted creature leaves the battlefield this turn, sacrifice this artifact. Activate only before blockers are declared.