Walkthrough: After completing
Captain Mina's Trial, you can head back to
Exeggutor Island to have your Poni Island Grand Trial with
Kahuna Hapu. If you didn't already know this, Kahuna
Hapu is a Ground Type Pokemon User and has access to Z Crystals. Defeat her to receive your next stamp of your passport - allowing Pokemon up to Level 80 to obey you - as well as Groundium Z.
Kahuna Hapu - Level 53 Golurk, Level 53 Gastrodon, Level 53 Flygon, Level 54 Mudsdale
Once you have completed your fourth and final Grand Trial, it is time to head to
Mount Lanakila to challenge the first ever
Alola Region Pokemon League.