Is Eidolon of Countless Battles legal in Standard, Modern, and Commander?

Eidolon of Countless Battles is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

Eidolon of Countless Battles

Q: What type of card is Eidolon of Countless Battles?

Eidolon of Countless Battles is an Enchantment Creature — Spirit. Its oracle text reads: "Bestow {2}{W}{W} (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.) This creature and enchanted creature each get +1/+1 for each creature you control and +1/+1 for each Aura you control. Power/Toughness: 0/0"

Enchantment Creature — Spirit

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.)