Mesmeric Fiend is a uncommon Creature — Nightmare Horror card from Masters 25 (A25), collector number 97. Current market price: $1.25 (foil $4.56), TCGplayer market prices via Scryfall.
When this creature enters, target opponent reveals their hand and you choose a nonland card from it. Exile that card. When this creature leaves the battlefield, return the exiled card to its owner's hand.