Ninja's Kunai is a common Artifact — Equipment card from Kamigawa: Neon Dynasty (NEO), collector number 252. Current market price: $0.24 (foil $0.25), TCGplayer market prices via Scryfall.
Equipped creature has "{1}, {T}, Sacrifice Ninja's Kunai: Ninja's Kunai deals 3 damage to any target." Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)