Grave Monstrosity

When Grave Monstrosity enters the battlefield, put the top four cards of your library into your graveyard.
Grave Monstrosity enters the battlefield with a +1/+1 counter on it for each creature card in your graveyard.
Whenever Grave Monstrosity attacks or blocks, remove two +1/+1 counters from it and create two 2/2 black zombie creature tokens.