Circu, Dimir Lobotomist is a rare Legendary Creature — Human Wizard card from Ravnica: City of Guilds (RAV), collector number 196. Current market price: $0.64 (foil $10.46), TCGplayer market prices via Scryfall.
Whenever you cast a blue spell, exile the top card of target player's library. Whenever you cast a black spell, exile the top card of target player's library. Your opponents can't cast spells with the same name as a card exiled with Circu.