Is Migratory Greathorn legal in Standard, Modern, and Commander?

Migratory Greathorn is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Pauper, Historic.

Migratory Greathorn

Q: What type of card is Migratory Greathorn?

Migratory Greathorn is a Creature — Beast. Its oracle text reads: "Mutate {2}{G} (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, search your library for a basic land card, put it onto the battlefield tapped, then shuffle. Power/Toughness: 3/4"

Creature — Beast

Mutate (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.)