Zargo, Keeper of Souls

Zargo, Keeper of Souls enters the battlefield
with a number of +1+1/ counters on it equal to
the number of zombies you control.
Whenever another Zombie enters the battlefield,
put a +1/+1 counter on Zargo, Keeper of Souls.
{u/b}{u/b},{t}, remove X +1/+1 counters from Zargo,
Keeper of Souls: Put X -1/-1 counters on target creature.