Mastermind Plum is a rare Legendary Creature — Human Wizard card from Ravnica: Clue Edition (CLU), collector number 3. Current market price: $5.30, TCGplayer market prices via Scryfall.
Whenever Mastermind Plum attacks, exile up to one target card from a graveyard. If an artifact card was exiled this way, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.") Whenever you cast a spell, if mana from a Treasure was spent to cast it, you draw a card and you lose 1 life.