Is Chittering Harvester legal in Standard, Modern, and Commander?

Chittering Harvester is legal in: Modern, Pioneer, Legacy, Vintage, Commander, Historic.

Chittering Harvester

Q: What type of card is Chittering Harvester?

Chittering Harvester is a Creature — Nightmare. Its oracle text reads: "Mutate {4}{B} (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, each opponent sacrifices a creature of their choice."

Creature — Nightmare

$0.22 ↗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.)