Morophon, the Boundless is a mythic Legendary Creature — Shapeshifter card from Modern Horizons Promos (PMH1), collector number 1p. Current market price: $8.68 (foil $12.52), TCGplayer market prices via Scryfall.
Changeling (This card is every creature type.) As Morophon enters, choose a creature type. Spells of the chosen type you cast cost {W}{U}{B}{R}{G} less to cast. This effect reduces only the amount of colored mana you pay. Other creatures you control of the chosen type get +1/+1.