In the Lower Realm, if there's anyone I'm not completely confident of dealing with, it would probably only be Ghost Father, the founder of the Heaven Mending Pavilion.
He was a truly prodigious individual, who originated from the upper realm sect Heaven Mending teaching. He was once its brightest core disciple and seen as the hope of the future of Heaven Mending teaching, with great hopes placed upon him.
In that magnificent era of gifted individuals, with just one man and one sword, he suppressed his talented peers so they could not raise their heads, outshining all others for a time. He had ignited the Divine Flame and entered the Godfire Realm even before he officially became an outcast.
In the long years of founding the Heaven Mending Pavilion in the Lower Realm, he should have made significant progress. It's highly possible that he's reached a terrifying realm by now, at the very least having achieved the position of a True God.