Is Pouncing Shoreshark legal in Standard, Modern, and Commander?

Pouncing Shoreshark is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Pouncing Shoreshark

Q: What type of card is Pouncing Shoreshark?

Pouncing Shoreshark is a Creature — Shark Beast. Its oracle text reads: "Mutate {3}{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.) Flash Whenever this creature mutates, you may return target creature an opponent controls to its owner's hand. Power/Toughness: 4/3"

Creature — Shark 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.)