Nightsky Mimic is a common Creature — Shapeshifter card from Eventide (EVE), collector number 91. Current market price: $0.18 (foil $0.97), TCGplayer market prices via Scryfall.
Whenever you cast a spell that's both white and black, this creature has base power and toughness 4/4 until end of turn and gains flying until end of turn.