Fenrir

Indestructible, Trample, Defender
Fenrir enters the battlefield with four +1/+1 counters. At the beginning of your upkeep double the number of +1/+1 counters on all creatures you control.
{8}{b}{g}: Monstrosity 10 (If this permanent isn't monstrous, put 10 +1/+1 counters on it and it becomes monstrous.)
When Fenrir becomes monstrous exile all other permanents.