Is Auspicious Starrix legal in Standard, Modern, and Commander?

Auspicious Starrix is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Auspicious Starrix

Q: What type of card is Auspicious Starrix?

Auspicious Starrix is a Creature — Elk Beast. Its oracle text reads: "Mutate {5}{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, exile cards from the top of your library until you exile X permanent cards, where X is the number of times this creature has mutated. Put those permanent cards onto the battlefield."

Creature — Elk Beast

$0.23 ↗20 similarCommander, Modern

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.)

Whenever this creature mutates, exile cards from the top of your library until you exile X permanent cards, where X is the number of times this creature has mutated. Put those permanent cards onto the battlefield.

Set Ikoria: Lair of Behemoths

Rarity Uncommon

Mana Value 5

Artist Lucas Graciano

Collector # 144