Soul of Theros

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.

Mystery Booster 2

Vigilance
{4}{W}{W}: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn.
{4}{W}{W}, Exile Soul of Theros from your graveyard: Creatures you control get +2/+2 and gain first strike and lifelink until end of turn.

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Magic 2015

Exiling the Soul from your graveyard is part of the last ability's activation cost. A player can't remove the Soul in response to prevent you from activating the ability.

You can activate the last ability only if the Soul is in your graveyard.