Is Soul of Theros legal in Standard, Modern, and Commander?

Soul of Theros is legal in: Modern, Pioneer, Legacy, Vintage, Commander.

What type of card is Soul of Theros?

Soul of Theros is a Creature — Avatar. Its oracle text reads: "Vigilance {4}{W}{W}: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn. {4}{W}{W}, Exile this card from your graveyard: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn."