Nemesis of Mortals (THS)

Nemesis of Mortals  (6) 
Creature — Snake (5/5) 
This spell costs  less to cast for each creature card in your graveyard.
: Monstrosity 5. This ability costs  less to activate for each creature card in your graveyard. (If this creature isn't monstrous, put five +1/+1 counters on it and it becomes monstrous.)