Outside, you'll find an unlikely force standing between you and Lusamine's residence at the end. Before proceeding, head all the way west, then up the stairs.
In the corner of this elevated area is a Full Heal. Next, run all the way east towards the opposite side. Phew, exercise is good for you! In the middle of the elevated area at the end is a Zygarde Cell (64) basking in the sun (or moon). After that, go back and begin to take on the grunts.
Team Skull Grunt
You should've encountered a few of these by now. Scare it away with Electric, Rock or Psychic-types. The latter should be mindful of Golbat's Leech Life though.
There's another foolish grunt up ahead.
Team Skull Grunt
Again, nothing new here. Send the gluttonous rat scurrying in record time with a Fighting-type; Bug or Fairy-types will also make short work of it.
The next grunt is smart. From here, continue north towards Gladion and Guzma, who are currently locked in battle. Despite Gladion's strength, you'll have to finish off the job.
Team Skull Boss Guzma
Persistent isn't he? This will be your third battle with Guzma and your toughest yet.
Like previously, he will lead with Golisopod and the exact same strategy applies. Pokemon weak to Bug moves should be benched since Golisopod can use First Impression the first turn it's out to deal big damage. Once the beast drops below half HP, it will switch out.
Masquerain is new; the evolved form of Surskit is a Bug and Flying-type so extremely susceptible to Rock-type moves. Fire, Electric and Ice-types moves will be very damaging as well. It has Intimidate so physical attackers should approach with caution.
Pinsir is also new; this rare Pokemon is a pure Bug-type, so it's weak to Fire, Rock and Flying-types. It knows Brick Break though, so Rock-types probably won't escape unscathed.
Finally, his Ariados is basically unchanged. It's again weak to Fire, Flying, Rock and Psychic-types. However all of its moves are super-effective against Psychic-types, so those Pokemon should steer clear if possible.
That's the second hurdle cleared. You're now free to enter the residence. Before that, if it's day time, head towards the west-most side of the residence. Sitting in the corner is another Zygarde Cell (65) waiting to be found.
Inside the residence, all the doors are barred, except the one to the north. Towards the east, it's incredibly hard to see, but there's a Zygarde Cell (66) below the small table. Beyond the door, you'll find what you were looking for, sort of.
After you've made all relevant preparations, follow Lusamine through the teleporter in the back. Grab the popcorn, then get ready for a battle with Madam President herself.
Aether President Lusamine
Lusamine is perhaps your toughest challenge so far; the youthful-looking president of the Aether Foundation has a mixture of powerful Pokemon carefully selected from her private collection.
Her first Pokemon, Clefable, is not to be taken lightly. The final evolution of Cleffa can use Cosmic Power to boost both defence stats and Metronome to use a completely random move. Defeat it with Poison or Steel-types or those that resist Fairy moves.
Next, she may send out Milotic. This gorgeous Water-type has high Special Defence, so hit it with physical Grass or Electric-type moves where possible. Pokemon that resist Water are good to have since Milotic can cause a lot of damage with Hydro Pump.
Mismagius is a potent special attacker with good speed and the Levitate Ability. Take it out with physical Dark or Ghost-type moves if you've got any. It also knows Fire and Rock-type moves so Pokemon weak to those moves need to be prepared.
Beware of Bewear; this fluffy monstrosity has the Fluffy Ability, which halves damage from contact moves, but gives it weakness to Fire-type moves. On top of that, it can use Baby-Doll Eyes to instantly drop your Pokemon's Attack. Slay it with Fairy, Psychic or Flying-types.
Finally, Lilligant has high Special Attack and decent Speed and a powerful Grass-type move in Petal Dance. Before that, it may use Teeter Dance to confuse your Pokemon or Stun Spore to paralyse them. Eradicate it with Fire, Flying, Bug or Ice-types.
Post-Battle Clean Up
After surviving Lusamine's onslaught, feel free to continue munching on your popcorn. The next day, you'll regain control in Lusamine's room. Follow Wicke's advice and exit the residence to meet Lillie and the others. Whoa, now that's a Z-powered form, alright.
That's not all for surprises, as Gladion hands you a rare Master Ball. If you've never gotten one before, it's a one-of-a-kind Poke Ball that captures any wild Pokemon with 100% success. We suggest saving it for a true emergency.
Afterwards, you'll be told to go to the docks. Return south to the entrance area; however, before heading for the elevator, carry on past towards the south exit. Unlike earlier, you won't be stopped by the employees. On the other side, you'll emerge at the front of Aether Paradise.
If it's night time, go all the way west. You can find a Zygarde Cell (67), the final one here, in the middle of the bridge that's closest to the Aether Foundation employee with the Miltank. Next, run all the way east to the opposite side. In the north-west corner is a Hyper Potion.
That's all for detours. Go back to the entrance area and use the elevator control to head to the dock area. There, you will find Lillie and Gladion waiting south-west from the elevator. Chat to Gladion to board the ferry to the next island.