Walkthrough: At the end of Vast Poni Canyon, directly before the Altar of the Sunne, is the next Island Trial apart of your Island Challenge. This Trial has nothing to do with Captain Mina; instead, this is the Original Trial Site where Trials first began long ago. All you must do is battle the Pokemon that appear in the path to the Dragonium Z, including Jangmo-o and Hakamo-o (both at Level 40).
As you reach the end of the path, but before you can collect Dragonium Z from the pedestal, you will be challenged by the Totem Pokemon Kommo-o, which will be at Level 49. All of its stats will be boosted by one stage as you enter the battle, with the ability to call on help from both Scizor (Level 46) and Noivern(Level 48). Defeat the Totem Pokemon and its allies to compelte the Trial and obtain Dragonium Z. After doing so, you will be able to advance to the Altar.