The Master of Keys is a mythic Legendary Enchantment Creature — Horror card from Duskmourn: House of Horror Commander (DSC), collector number 4. Current market price: $2.80 (foil $0.82), TCGplayer market prices via Scryfall.
Flying When The Master of Keys enters, put X +1/+1 counters on it and mill twice X cards. Each enchantment card in your graveyard has escape. The escape cost is equal to the card's mana cost plus exile three other cards from your graveyard. (You may cast cards from your graveyard for their escape cost.)