Sword of Once and Future is a mythic Artifact — Equipment card from March of the Machine (MOM), collector number 265. Current market price: $5.17 (foil $5.36), TCGplayer market prices via Scryfall.
Equipped creature gets +2/+2 and has protection from blue and from black. Whenever equipped creature deals combat damage to a player, surveil 2. Then you may cast an instant or sorcery spell with mana value 2 or less from your graveyard without paying its mana cost. If that spell would be put into your graveyard, exile it instead. Equip {2}