As an additional cost to cast Toxic Deluge, pay X life.
All creatures get -X/-X until end of turn.
6/8/2016 The payment of life is an additional cost. You lose the life even if Toxic Deluge is countered.
6/8/2016 If you cast Toxic Deluge without paying its mana cost, you’ll still choose a value for X and pay X life. This is because it doesn’t have in its mana cost.
6/8/2016 All creatures on the battlefield when Toxic Deluge resolves are affected. Ones that enter the battlefield or become creatures later in the turn are not.