Shadow Alley Swindler

When Shadow Alley Swindler enters the battlefield, each player discards a nonland card. Then, each player with the highest total converted mana cost or tied for highest total converted mana cost of every card in his or her graveyard gains 4 life and each other player loses 2 life.
{2}{b}{b}, Pay 3 life: Return Shadow Alley Swindler from your graveyard to the battlefield tapped. Activate this ability only any time you could cast a sorcery.