Slagwurm Armor is a common Artifact — Equipment card from Mirrodin (MRD), collector number 243. Current market price: $1.05 (foil $7.78), TCGplayer market prices via Scryfall.
Equipped creature gets +0/+6. Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery. This card enters unattached and stays on the battlefield if the creature leaves.)