Ronin Warclub is a uncommon Artifact — Equipment card from Betrayers of Kamigawa (BOK), collector number 158. Current market price: $0.36 (foil $2.90), TCGplayer market prices via Scryfall.
Equipped creature gets +2/+1. Whenever a creature you control enters, attach this Equipment to that creature. Equip {5} ({5}: Attach to target creature you control. Equip only as a sorcery.)