Rabreth, the Aberrant Mind

Shadow (This creature can block or be blocked by only creatures with shadow) Whenever this creature deals damage to an opponent, you may pay {2} {U/B}. If you do, it gets a +1/+1 counter. This ability only triggers once per turn. When this creature dies, return this creature to the battlefield transformed under it’s owners control with X sight counters on it, where X is the amount of +1/+1 counters on it.