Is Nighthowler legal in Standard, Modern, and Commander?

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

Nighthowler

Q: What type of card is Nighthowler?

Nighthowler is an Enchantment Creature — Horror. Its oracle text reads: "Bestow {2}{B}{B} (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)Nighthowler and enchanted creature each get +X/+X, where X is the number of creature cards in all graveyards."

Enchantment Creature — Horror

Bestow (If you cast this card for its bestow cost, it's an Aura spell with enchant creature. It becomes a creature again if it's not attached to a creature.)<br>Nighthowler and enchanted creature each get +X/+X, where X is the number of creature cards in all graveyards.