Peppermint, Unassuming Horror

Whenever an opponent casts a spell that targets one or more creatures, if Peppermint wasn't a target of that spell, put a +1/+1 counter on Peppermint.
As long as Peppermint has three or more
+1+1 counters on it, it's a Demon Horror
with hexproof, flying, and trample.