Banshee's Blade is a uncommon Artifact — Equipment card from Mirrodin (MRD), collector number 144. Current market price: $0.30 (foil $20.55), TCGplayer market prices via Scryfall.
Equipped creature gets +1/+1 for each charge counter on this Equipment. Whenever equipped creature deals combat damage, put a charge counter on this Equipment. Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)