Master of Rot

Whenever Master of Rot blocks or becomes blocked by a creature, that creature gains a fester counter.
At the beginning of each players upkeep, creatures get a -1/-1 counter for each fester counter on them.
Whenever a creature dies from a fester counter, that creature comes under your control as a black zombie in addition to its other colors and types.
{t}{b}{b}{b} Target creature gains a fester counter