Kalathar, Endless Hordes

As an additional cost to Kalathar, Endless Hordes sacrifice X creatures.
When Kalathar, Endless Hordes enters the battlefield exile all cards in graveyards, for each creature exiled this way put a +1/+1 counter on Kalathar, Endless Hordes.
"I can hear them coming, and I have never been more afraid."
-Last words, Shivik General