Skullkeeper Troll

Skullkeeper Troll enters the battlefield with a
+1/+1 counter.
Whenever a creature dealt damage by Skullkeeper
Troll this turn dies, double the number of +1/+1 counters on it.
{2}{g}{g}: Monstrosity 2. If this creature isn't
monstrous, put a +1/+1 counter on it and it becomes monstrous.)