Soul of Theros is a mythic Creature — Avatar card from Magic 2015 (M15), collector number 34. Current market price: $0.30 (foil $1.78), TCGplayer market prices via Scryfall.
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.