Volokthug, Brimstone Demon

When casting this, you may pay X life. For every three life paid, this spell costs {2} less.
Haste, first strike
At the beginning of your upkeep, you may X life. If you do, Volokthug, Brimstone Demon gets that many +1/+1 counters.
{t}, remove X +1/+1 counters: Deal X damage to any target.