Serrek Ik-van-hal

Indestructible, lifelink
Whenever a creature dies, target creature you control descends. (A creature that descends gets a -1/-1 counter and, for as long as it remains on the battlefield, is a black Demon in addition to its other colors and types and has deathtouch, and lifelink.)
{b}: Add {b} to your mana pool for each creature you control that has descended.