Unseal the Necropolis is a common Instant card from March of the Machine (MOM), collector number 128. Current market price: $0.25 (foil $0.19), TCGplayer market prices via Scryfall.
Each player mills three cards. Then you return up to two creature cards from your graveyard to your hand. (To mill three cards, a player puts the top three cards of their library into their graveyard.)