Vex,The Gloomist

Fear
You may pay {x} with your life total.
Doom:{2}{x}{t},Tap {x} creatures until end of turn.
Gloom:Whenever Vex,The Gloomist attacks deal {x} damage to target creature or player where {x} is the number of creatures you've tapped this turn
{3}{b}:Untap Vex The Gloomist