Darkmountain, Syv's Domain

Darkmountain, Syv's Domain enters the battlefield tapped.
{t}: add {b} or {r} to your mana pool. You may put a -1/-1 counter on target creature an opponent controls. If you do, put a -1/-1 counter on target creature you control.
Syv cares not what he does to the plane of Fvoran, only that he gains enough power to steal himself a planeswalker spark.