Location: Route 5

You first encounter Gladion in Route 5 where you encounter him battling with Hau. He managed to defeat Hau and doesn't understand why Hau isn't taking it seriously and is instead finding his loss enjoyable. He then challenges you

Team Skull Gladion	Zubat	Type: Null
Battle Type Items	Level 17	Level 18
	Attacks: Bite Wing Attack	Attacks: Tackle Pursuit
	Hold Item: No Item	Hold Item: No Item

Defeat him and he will explain how he has been doing odd jobs for Team Skull. Then, Team Skull appear and chastise Gladion for stopping them from stealing the local Totem Pokémon and how despite Guzma liking him, he will never be a part of Team Skull. He will then leave.

Location: Royal Avenue

Your next encounter with Gladion is in the Battle Royal Dome in Royal Avenue. He originally goes there to just bury his sorrow in the crowd, but when The Masked Royal spots you and Hau there, he offers a Battle Royal and then invites Gladion to be the fourth person

Team Skull Gladion	Type: Null
Battle Type Items	Level 19
	Attacks: Tackle Pursuit
	Hold Item: No Item

Location: Route 8

Your next encounter with Gladion is a rather abrupt one. In the Motel in Route 8, you will learn that the person renting the room has paid up for a long time in advance. Go inside and you'll find that it is Gladion. Speak to him and he will simply utter his request for you to leave.

Location: Route 13

When you reach Route 13, Gladion will appear in front of you and Hau again, this time mentioning that Team Skull is looking for a Pokémon called Cosmog. Asking if you know anything about it, Hau acts coy causing Gladion to realise you do know about it. He explains how Cosmog may not be powerful but it can bring powerful Pokémon to Alola which would cause disaster and begs for you to protect Cosmog above all else. He then leaves.

Location: Aether House

After you have defeated Guzma in the Shady House, when you return to the Aether House in Route 15 to find Lillie has been kidnapped. He overhears you mention that Lillie took Cosmog and is angry that you and Hau allowed for her and Cosmog to be captured and challenges you to a battle.

Team Skull Gladion	Golbat	Sneasel	Type: Null
Battle Type Items	Level 37	Level 37	Level 38
	Attacks: Acrobatics Poison Fang	Attacks: Icy Wind Metal Claw Feint Attack Quick Attack	Attacks: Pursuit Crush Claw X-Scissor
	Hold Item: No Item	Hold Item: No Item	Hold Item: No Item

After defeating him, he will apologise for how he acted and mention that you have to go to the Aether Foundation with him in order to save Lillie. Go to the ferry dock in Malie City and he'll be waiting for you and Hau.

Location: Aether Paradise

In the Aether Paradise, you, Gladion & Hau battle through the various Aether employees in a bid to rescue Lillie. This requires you to go to the secret laboratories in the basement of the building. However, the lift won't go down so you need to go up where you battle with Faba, with Gladion by your side. Soon after that, Wicke appears and indicates that she has history with Gladion, calling him master. Going down to the basement, he asks you not to enter the Secret Laboratory A, but to go to Secret Laboratory B. Return upwards and you'll be ambushed yet again, this time where you have a Multi Battle with Gladion

Team Skull Gladion	Golbat	Type: Null
Battle Type Items	Level 38	Level 39
	Attacks: Acrobatics Poison Fang	Attacks: Pursuit Crush Claw X-Scissor
	Hold Item: No Item	Hold Item: No Item

Location: Aether Paradise

Fighting through the rest of the Aether Foundation, you will come topside where Gladion will see a line of Team Skull members and barge through them, rushing to Guzma in order to challenge him, but he loses and starts feeling down that all his training and effort was for nothing, with Guzma condescending him in the process.

After you defeat Guzma, he requests you save Lillie and you go in to stop Lusamine. During this, Lusamine reveals that she is Gladion & Lillie's mother and how disappointed she is in them for stealing her Pokémon, Type: Null and Lillie. Then, forcing Cosmog to create a wormhole, her plan comes to fruition, opening Ultra Wormholes throughout the region. Gladion suggests the three of you stop them, with him and Type: Null taking on the Ultra Beasts while you face Lusamine and Hau takes on Guzma. Lusamine then disappears into the wormhole.

After that situation, Gladion thanks you for your help and gives you the Moon Flute/Sun Flute in order to go find Solgaleo/Lunala to bring his mother home. He also gives you the Master Ball. He then takes you and Lillie to Poni Island and suggests looking for the Kahuna to get their assistance.

Location: Mount Lanakila

After stopping the situation with Team Skull & Lusamine, when you go to take on the Pokémon League, Gladion will appear, thanks you for what you did, and challenges you to a battle to test his strength and understand why Lillie calls you the best trainer in the world. His Type: Null will have evolved and will be of the type that is super effective against your Starter Pokémon.

Pokémon Trainer Gladion	Crobat	Weavile	Lucario	Silvally
Battle Type Items	Level 52	Level 52	Level 52	Level 53
	Attacks: Acrobatics Cross Poison	Attacks: Ice Shard Night Slash Metal Claw	Attacks: Aura Sphere Metal Claw Quick Attack	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Fire Memory
Rowlet Chosen

Pokémon Trainer Gladion	Crobat	Weavile	Lucario	Silvally
Battle Type Items	Level 52	Level 52	Level 52	Level 53
	Attacks: Acrobatics Cross Poison	Attacks: Ice Shard Night Slash Metal Claw	Attacks: Aura Sphere Metal Claw Quick Attack	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Water Memory
Litten Chosen

Pokémon Trainer Gladion	Crobat	Weavile	Lucario	Silvally
Battle Type Items	Level 52	Level 52	Level 52	Level 53
	Attacks: Acrobatics Cross Poison	Attacks: Ice Shard Night Slash Metal Claw	Attacks: Aura Sphere Metal Claw Quick Attack	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Grass Memory
Popplio Chosen

Location: Aether Paradise

After you have stopped Lusamine's plans and rescued her from the Ultra Space and beaten the Elite Four, you can return to the Aether Paradise and go up to the Conservation Area where you will find Gladion. Thankful for your help, Gladion will give you one of the other Type: Null that the Aether Foundation created. He will also give you all the Memory items for use when it evolves into Silvally.

Type: Null Level 40

OT: Yours ID: Yours Ability: Battle Armor Hold Item: None

??? Nature. Date of Receiving Aether Foundation. Caught at Lv. 40

Crush Claw Scary Face X-Scissor Take Down

Pokémon: Pokémon League

Details:
The Pokémon League is the next and final place that you will find Gladion. During subsequent bouts against the Elite Four, Gladion will appear randomly as one of the many challengers to the Champion title

Pokémon Trainer Gladion	Crobat	Weavile	Porygon-Z	Lucario	Silvally
Battle Type Items	Level 63	Level 63	Level 63	Level 63	Level 63
	Attacks: Acrobatics Cross Poison X-Scissor Steel Wing	Attacks: Ice Shard Night Slash Brick Break Shadow Claw	Attacks: Tri Attack Dark Pulse Ice Beam Thunderbolt	Attacks: Aura Sphere Flash Cannon Extreme Speed Psychic	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Fire Memory
Rowlet Chosen

Pokémon Trainer Gladion	Crobat	Weavile	Porygon-Z	Lucario	Silvally
Battle Type Items	Level 63	Level 63	Level 63	Level 63	Level 63
	Attacks: Acrobatics Cross Poison X-Scissor Steel Wing	Attacks: Ice Shard Night Slash Brick Break Shadow Claw	Attacks: Tri Attack Dark Pulse Ice Beam Thunderbolt	Attacks: Aura Sphere Flash Cannon Extreme Speed Psychic	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Water Memory
Litten Chosen

Pokémon Trainer Gladion	Crobat	Weavile	Porygon-Z	Lucario	Silvally
Battle Type Items	Level 63	Level 63	Level 63	Level 63	Level 63
	Attacks: Acrobatics Cross Poison X-Scissor Steel Wing	Attacks: Ice Shard Night Slash Brick Break Shadow Claw	Attacks: Tri Attack Dark Pulse Ice Beam Thunderbolt	Attacks: Aura Sphere Flash Cannon Extreme Speed Psychic	Attacks: Crunch Crush Claw X-Scissor Multi-Attack
	Hold Item: No Item	Hold Item: No Item	Hold Item: No Item	Hold Item: Steelium Z	Hold Item: Grass Memory
Popplio Chosen