Riblee, Shadowed Mentor

When one or more creatures you control attack, put a Hubris counter on all attacking creatures. (+1/+1, if a creature has 3 or more hubris counters, sacrifice it at the end of your combat step)

At the beginning of your end step, if there are 4 or more hubris counters among creatures you control, you may transform Riblee, Shadowed Mentor.