Xorafen, Herald of Death

Xorafen, Herald of Death enters the battlefield with 20 +1/+1 counters on it
Whenever Xorafen, Herald of Death is dealt damage, you may prevent X damage, If you do, Remove X +1/+1 counters from Xorafen, Herald of Death and create X 1/1 Skeleton creature tokens
{b}, Sacrifice a skeleton: Put a +1/+1 counter on Xorafen, Herald of Death