Hydra of Endless Battle

This card may block any number of creatures
This creature enters the battlefield with 3 hydra counters on it. Whenever this creature blocks a card, remove a counter for each card blocked, then at the end of turn double the remaining counters and add counters equal to the amount lost this way. If this creature destroys another creature, add a counter for each and then double the counters. This card cannot be destroyed during anyturn if a counter was on this card