Mistform Seaswift is a common Creature — Illusion card from Legions (LGN), collector number 45. Current market price: $0.13 (foil $0.44), TCGplayer market prices via Scryfall.
Flying {1}: This creature becomes the creature type of your choice until end of turn. Morph {1}{U} (You may cast this card face down as a 2/2 creature for {3}. Turn it face up any time for its morph cost.)