The League was the soul, the Hexing magics were the bones, and the Mountains and Seas were the flesh!
The doctrines of the League of Demon Sealers held sway, which were the same as the doctrines espoused by Meng Hao. By following such precepts, he had become the Crown Prince of the Mountain and Sea Realm. The year he became part of the League of Demon Sealers, he was acknowledged as the future Lord of the Mountain and Sea Realm.
The first version of the Mountain and Sea Realm was forged by Nine Seals, who also left behind the League of Demon Sealers as his legacy. Now Meng Hao was using that legacy to remould the Mountain and Sea Realm into something new.
Anyone who became a Mountain and Sea Lord had to become a successor of the League of Demon Sealers. Furthermore, anyone who wanted to be the Lord of the Mountain and Sea Realm itself had to master all of the Nine Hexes.
As for Transcendence... that would depend on one's personal fortune.