Devilish Guardian

Flying
Grovel (When this creature enters the battlefield, you may pay {x}. If you do, put X -1/-1 counters on it and X +1/+1 counters on target creature.)
As long as Devilish Guardian has two or more
-1/-1 counters on it, it gains vigilance and fear (It can't be blocked except by artifact creatures and/or black creatures.)