In the north end of Po Town, you find Shady House, defended by many Team Skull Grunts.
Explore Shady House
Go all the way to the left and go through the door in the left wall. There is an Ice Stone above the empty swimming pool.
Go back into Shady House, then go through the door to the left of the stairs. In this room, you can battle the Grunt to the right of the fireplace. She has a level 38 Trubbish and a level 38 Houndour. You get 1216 Pokédollars for winning.
Keep going to the right, through a couple of doors, to find a kitchen with a note on the floor. Read the note to find out today's Team Skull password: Tapu Cocoa. It also says that a true Team Skull member always answers questions with "No!"
Go south in the kitchen to find a Heal Powder.
Go back to the first room of the mansion. To the left, you can battle a Team Skull Grunt who has a level 38 Salandit and a level 38 Fomantis. You get 1216 Pokédollars for winning.
Go through the bottom-left door to find a Max Revive. Then go back out and go through the upper-left door to find another note with today's Team Skull password: Poison Jab.
Back in the first room of the mansion, go to the right of the stairs and you can battle a Team Skull Grunt who has a level 38 Drowzee. You get 1216 Pokédollars for winning.
Go up the stairs.
Go to the left, then go north and go through the upper-left door. You find TM36 Sludge Bomb.
Go out, then if you go through the next door on the left, you have to battle a Team Skull Grunt who has a level 38 Alolan Rattata. You get 1216 Pokédollars for winning. After that, you have to battle a Team Skull Grunt who has a level 38 Alolan Raticate. You get 1216 Pokédollars for winning.
Go back to the hallway, and go through the bottom-left door. You have to battle a Team Skull Grunt who has a level 38 Haunter and a level 38 Grimer. You get 1216 Pokédollars for winning.
Go to the left of that Grunt to get an Iron. Then check to the right of the Grunt to find another note with this month's Team Skull password: Bounsweet.
Leave this room, then go to the right and you can battle a Team Skull Grunt who has a Scraggy. You get 1216 Pokédollars for winning.
Go to the right and talk to the Grunt who is standing guard at the door. Give him the three passwords (Poison Jab, Bounsweet, Tapu Cocoa) and when he asks if you are sure, say "No!" He will move aside.
Go through the door that the Grunt was blocking.
Go to the right and get the Escape Rope to the right of the open window.
Below that, you can battle a Team Skull Grunt who has a level 38 Spinarak, a level 38 Golbat, and a level 38 Pawniard. You get 1216 Pokédollars for winning.
Now go north through the open window, then go north and go through the door that the two Grunts are guarding.
Step forward to start a cut scene. You will battle Team Skull Boss Guzma. He has a level 41 Golisopod, a level 41 Pinsir, and a level 41 Masquerain. You get 4920 Pokédollars for winning.
Guzma will leave. Before you leave, check the treasure chest to get a Buginium Z. You can sit in Guzma's throne if you want.
Now go back the way you came, or just use an Escape Rope to leave the mansion. Go south from the mansion and there will be a cut scene. After that, go to Tapu Village and go north from there to Aether House.
Inside, after a cut scene, Gladion storms in and battles you. Team Skull Gladion has a level 42 Golbat, a level 42 Zoroark disguised as Type: Null, and a level 43 Type: Null. You get 3440 Pokédollars for winning.
Afterward, Gladion insists that you go with him, so say Yes if you are ready. If you're not ready, then you can say no and make preparations, then go to Malie City and go east to the ferry terminal to meet up with Gladion.
After a cut scene, the Ula'ula Island Kahuna challenges you. Island Kahuna Nanu has a level 43 Sableye, a level 43 Krokorok, and a level 44 Alolan Persian. You get 7040 Pokédollars for winning.
Afterward, he heals your pokémon and gives you the Dark-type Z-Crystal. You also get a new stamp for your Trainer Passport, which causes all pokémon up to level 65 to obey you.
Following a cut scene, you arrive in Aether Paradise.