Author of Shadows is a rare Creature — Shade Warlock card from Commander 2021 (C21), collector number 35. Current market price: $0.59, TCGplayer market prices via Scryfall.
When this creature enters, exile all opponents' graveyards. Choose a nonland card exiled this way. You may cast that card for as long as it remains exiled, and you may spend mana as though it were mana of any color to cast that spell.