Grim Giganotosaurus

{10}{B}{G}: Monstrosity 10. This ability costs {1} less to activate for each creature with power 4 or greater your opponents control. (If this creature isn't monstrous, put ten +1/+1 counters on it and it becomes monstrous.)
When Grim Giganotosaurus becomes monstrous, destroy all artifacts and creatures other than Grim Giganotosaurus.