Festering Warlock

Painborn (Each 1 life you pay while casting this spell pays for {c}. It eneters the battlefield with a -1/-1 counter for each 1 life paid this way)
{t}: Put a poison counter on up to X target creatures and players, where X is Festering Warlock's power. Put a -1/-1 counter on Festering Warlock.
Pay 2 life: remove a -1/-1 counter from Festering Warlock.