After passing through the rocky Route 12 and the oasis in Route 13, you reach Tapu Village.
Tapu Village
Go west to reach Tapu Village. Go to the left and you meet Hau. You won't be able to go north from here because the Pokémon League is still under construction.
After the cutscene, go to the left and enter the Pokémon Center.
A hiker in the Pokémon Center named Sill will trade you his Graveler, Veler, if you trade him a Haunter. You can get a Haunter by catching Gastly in Memorial Hill and raising it to level 25.
Outside, if you go straight down from the Pokémon Center, you find another green sparkle for the Zygarde Cube.
First, you should go to Route 15. Go west from Tapu Village to get there.
Route 15
Go north to the Aether House and go inside. Hau joins you, then you have to battle Preschooler Hunter, who has a level 30 Elekid. You get 360 Pokédollars for winning.
After the cutscene, you can go into the room on the left to find a green sparkle for the Zygarde Cube in the upper-left corner.
Outside, you have to battle a Team Skull Grunt that has a level 33 Drowzee. You get 1056 Pokédollars for winning.
Afterward, you get 5 Luxury Balls.
Now go south to return to Tapu Village, then go south and approach Acerola, then go south to reach Route 14.
Route 14
To the left of the entrance, there is a hidden Pearl.
In the west side of the water, to the right of the stone platform, you can battle Swimmer Keoni. He has a level 31 Pyukumuku. You get 744 Pokédollars for winning.
Go onto the stone platform to get TM30 Shadow Ball.
Go back onto the beach. Southeast of the route entrance, you can battle Fisherman Hisato. He has a level 30 Feebas and a level 31 Gyarados. You get 992 Pokédollars for winning.
You can go up onto the broken road, then go east to get a Max Potion.
Go to the right to jump down the one-way ledge. Then go downward down the ramp and you can battle Collector Kawika. He has a level 30 Togedemaru and a level 31 Gabite. You get 992 Pokédollars for winning.
There is a hidden Big Pearl to the left of the ramp.
Keep going to the right and you will find a green sparkle for the Zygarde Cube on the far right side of the beach.
Now approach Acerola, who is standing in front of the stairs near the east side of the beach. Then go up the stairs.
Acerola will tell you that you have to go into the building and take a picture of the Totem Pokémon with the Poké Finder. However, the Totem Pokémon likes to hide, so you should investigate any weird happenings inside.
Acerola adds a special mode to your Poké Finder that you can only use in this trial.
If you are ready, go into the building.
Abandoned Thrifty Megamart
Go into the building and follow the path until you see a conveyor belt start moving by itself. Check on it and use the Poké Finder. Aim it upward to find a Gastly. Take a picture and you will battle the level 30 Gastly.
Afterward, a Pikachu will go running past down below, so follow it. You will find a shopping cart moving on its own. Go up to it and check on it, then use the Poké Finder. Aim it upward and take a picture of the Haunter. You will have to battle the level 30 Haunter.
Then you will see a Pikachu going upward, so go to the right, then go upward, and follow the path until you see some floating dolls. Go up and check on them, then use the Poké Finder. Aim the Poké Finder around until you find the Gengar. Take its picture, and you will have to battle the level 30 Gengar.
After that, you will see a Pikachu to the left, going upward to some doors. Go to those doors. They will unlock on their own. Open the door and the Poké Finder will automatically start. The pokémon is behind you! Turn the Poké Finder around and take a picture of the pokémon. You will have to battle it.
The Totem Mimikyu is level 33. It is weak to Ghost and Steel attacks. It can call Haunter into battle. The first time you hit Totem Mimikyu, it will do no damage, but it will break the Mimikyu's diguise so that you can damage it from then on.
Afterward, Acerola gives you Ghostium Z, and you can now catch pokémon inside the trial site. She also gives you 10 Dusk Balls.
Now that you have completed the Ghost trial, you can enter Haina Desert. There is a Z-Crystal there. Or you can go to Route 15 now and visit Haina Desert some other time.