Mistway Spy is a uncommon Creature — Merfolk Detective card from Murders at Karlov Manor (MKM), collector number 65. Current market price: $0.11 (foil $0.27), TCGplayer market prices via Scryfall.
Flying Disguise {1}{U} (You may cast this card face down for {3} as a 2/2 creature with ward {2}. Turn it face up any time for its disguise cost.) When this creature is turned face up, until end of turn, whenever a creature you control deals combat damage to a player, investigate.