Blasecube, Corrupted Avenger

Whenever Blasecube, Corrupted Avenger enters the battlefield or another creature dies, place a +1/+1 counter on Blasecube, Corrupted Avenger.
{10}: You may exile up to 10 creatures from your graveyard to reduce the cost of this ability by {1} each. Return all creatures from all graveyards into their owners battlefield. Then, if you exiled any number of creatures to activate this ability, return them to your graveyard.