Trumpeting Gnarr is a uncommon Creature — Beast card from Ikoria: Lair of Behemoths (IKO), collector number 307. Current market price: $0.20 (foil $0.37), TCGplayer market prices via Scryfall.
Mutate {3}{G/U}{G/U} (If you cast this spell for its mutate cost, put it over or under target non-Human creature you own. They mutate into the creature on top plus all abilities from under it.) Whenever this creature mutates, create a 3/3 green Beast creature token.