Vex,The Gloomist

Fear
For each {x} in a cost, you may pay life rather than pay that mana.
Doom -{2}{x}{t}:Tap X target creatures.
Gloom -Whenever Vex,The Gloomist attacks it deals
X damage to target creature or player where X is the amount of creatures you've tapped this turn.
{3}{b}:Untap X Creatures.