Marowak was shown to be troublesome since it caused some chaos to other Pokémon at the festival. After getting defeated by Kiawe, nonetheless, its problematic side has begun to converge as it has started to respect his skills as a battler, which is one of the reasons it chose him to be its trainer with the other reason being it can learn a lot from him. Still, it doesn't trust Turtonator much owing to the experience of being defeated by Turtonator as well as its bellicose personality and always wants to fight with Turtonator due to seeing it as a rival, though fortunately their relationship has advanced through the course of the series. Also, Marowak even became friends with the Pokémon owned by its Trainer's friends.
It loves to dance around with its bone, especially when it's thrilled.
Marowak also had a short rivalry with a fellow Marowak from the Kanto region only to be restrained by both Brock and Kiawe. It also had a mischievous side by attacking towards the wild Onix's head using its bone when Brock tries to calm it down.
Marowak is later shown to have a fear of water as it wouldn't jump in the pool and play with its friends.
Marowak, as a wild Pokémon, first appeared in the crowning ceremony and stole the crown that Olivia was going to crown Litten with its bone before causing more havoc and running away. With the help of three hikers, Kiawe managed to find Marowak, who was practising its dance and challenged it to a battle. However, thanks to the crown it had stolen, Marowak was able to dodge Turtonator's attacks as well as Turtonator's Z-Move and defeated Turtonator, which caused Turtonator to have severe injuries. After Turtonator was recovered and had a practice match with Pikachu the day before, Kiawe challenged Marowak, who wounded the hikers' Magmar, to a rematch in which it got defeated this time. Impressed by Kiawe's skills, Marowak asked if it could come with him after it returned the crown. Kiawe accepted its offer and caught it thus adding it to his team
, though it still wanted to continue fighting with Turtonator and got stuck at Tutornator's belly-hole until Kiawe helped it to get out. Then it got crowned in the ceremony and was ready for a photo with its new trainer, Turtonator and its trainer's friends with their Pokémon which the hikers' appeared in a few of the photos jumping in somewhere in them.
Marowak and Turtonator were seen arguing and later they began to fight, and Marowak got its head stuck in Turtonator's belly-hole and Kiawe recalled them back into their Poké Balls. It was then seen eating its food with the other Pokémon while glaring at Turtonator.
At Prof. Oak's lab, Marowak met a fellow Kantonian Marowak and the two soon was about to fight. Togedemaru was unable to calm both them down and got chased instead. Pikachu had enough with the chaos and used his electricity to shock everyone, causing Marowak and Popplio to get separated from the group. Then, when Ash, Sophocles, Kiawe and Brock encountered an Onix, Marowak suddenly appeared and threw its bone at the Onix, enraging the wild Onix and the guys had to run. After Marowak and its other friends were saved by Ash's Lycanroc, Brock's Crobat and Misty's Staryu, Jigglypuff made everyone fell asleep, thus it got its face drawn by Jigglypuff.
Marowak watched the battle between Kiawe and Brock at Cerulean City Gym. It was furious to see Kiawe's loss to Brock and his Steelix and it continued to scold him and Turtonator even after it headbutted both of them.
Marowak was later used in Ultra Deep Sea to battle alongside Turtonator, against Lusamine's Salazzle while rescuing Lusamine. Marowak and Turtonator continued their battle with Salazzle, but they were immediately halted after Ash and Pikachu freed Lusamine from Nihilego's mind-control.
Sometime later, Marowak helped Kiawe and his classmates complete several Ultra Guardian missions and helped Ultra Beasts return home. And in the process it meets a new friend who is also an Ultra Beast, Ash's Poipole.
Sometime later, Marowak was used to battle Masked Royal and his Incineroar at the Battle Royal Dome along with Sophocles' Charjabug, and Ash's Litten. But all three of them were defeated by Incineroar's super-powerful Darkest Lariat attack.
Marowak later battled against Viren in order to protect Kiawe's farm from being bulldozed. It managed to defeat Viren's underlings' Roggenrola and Boldore with Turtonator's help, but Turtonator was knocked out by Electivire's Thunder while protecting Mimo. Marowak and Kiawe attempted to finish the battle with their Z-Power, but it failed when Marowak didn't finish syncing with its trainer, which resulted in Electivire winning the battle. During the night, Kiawe confessed to Marowak that the reason they couldn't pull the Z-Move off was because he doubted Marowak's ability in using it as well as not having enough trust in their bond. Kiawe and Marowak decided to spend the night training in hopes of perfecting the Z-Move and strengthen their friendship.
The next day, Viren and his underlings came and are challenged to a rematch. Now, with its newfound strength in their bond, Marowak battle Electivire again and managed to defeat it with its fully mastered Z-Move, Inferno Overdrive.
Marowak was later used in a practice battle with Ash's Pikachu. But when they tried to perform their Z-Moves, the strange phenomenon that's been affecting the adults in Alola absorbed their Z-Power, making them weak and invulnerable. During an Ultra Guardians mission at the Altar of the Sunne in Poni Island, Marowak combined its Z-Power with Ash's Pikachu, Lana's Popplio, and Gladion's Lycanroc to power up Faba's machine to clear the skies.
After travelling through the Ultra Wormhole, the Ultra Guardians enter a strange dimension that used to be the home of Ash's Poipole. As they search for Necrozma, they are attacked by wild Poipole, but Ash's Poipole stopped them and told them they're not bad guys. Just then, an old and weak Naganadel comes out and the Ultra Guardians rush over to help it, much to Gladion's dismay. After nursing Naganadel, Marowak, along with the other Pokémon, listened to its story about Necrozma's connection with the Blinding One, Ash's Poipole, and their homeworld. They learned that the reason why Necrozma possessed Nebby and Lunala was because it wanted a huge amount of Ultra Aura to restore its Ultra form and replenish Poipole's world due to the lack of its light. They also learn that Necrozma is actually the Blinding One the legends spoke about. Suddenly, the gang hears a crash outside and see Lunala still fighting with Necrozma. Gladion and Silvally attempt to defeat Necrozma, but they were immediately stopped by Ash and his classmates. They tell Gladion that if he drives Necrozma away, Naganadel, Poipole and its homeworld will die from the lack of light. Ash and the gang decide that the best way to save Nebby, help Necrozma, and replenish Poipole's world is to transfer their Z-Power. Together, Ash, Gladion, Kiawe, and Lana fired their Z-Moves at Necrozma.
But unfortunately for them, their attempt was unsuccessful. Instead of freeing Nebby, the Z-Moves only increased Necrozma's power and made it stronger. Necrozma goes to attack everyone, but is held off by Lunala. The Ultra Guardians learned from Professor Burnet that according to legend, Solgaleo, Lunala, and the people and Pokémon of Alola shared their Z-Power with the Blinding One when it lost its light. So, the Ultra Guardians as well as with the combined Z-Power of everyone in Alola as well as the Team Rocket Trio, the Guardian Deities, and the Island Kahunas, Necrozma gained enough light to free Nebby from its grasp. But despite their successful attempt, Necrozma became angry at their interference and attacked the Ultra Guardians in a blind rage. Hala, Olivia, and Nanu save the Ultra Guardians by transferring their Z-Power to Necrozma. But Necrozma wasn't giving up just yet. Necrozma then goes after Nebby and Lunala again, only to be held off by Gladion and Silvally. With Necrozma distracted, Lunala gave Gladion the Lunalium Z and Nebby recovers. Just as Necrozma was about to attack again, Ash and Gladion combined Nebby and Lunala's Z-Moves to help Necrozma provide enough Ultra Aura to return into its heroic Ultra form. Necrozma then uses its power to restore Poipole's homeworld to its previous majesty and disappears just as the solar eclipse ended. As they go to leave, the Ultra Guardians bid a tearful farewell to Poipole and returned to Alola, while also witnessing Necrozma appearing above them in the sky.
Later, Marowak befriends a messy-haired Eevee, who was later nicknamed Sandy and would join their group of friends as one of Lana's Pokémon, that came to Alola from across the sea. After Eevee touched Turtonator spikes, Marowak scolded him for touching them but laugh about it when Pikachu only got burned halfway. Marowak played with his new friend until it was time for him and Turtonator to head back to Kiawe with their friends as they also needed to return to their trainers.
Upon at arriving at Poni Island, Marowak was in a battle along with Turtonator against Ash's Pikachu and Torracat, but was caught by Tapu Fini, along with the others, but luckily was free thanks to Kiawe.
While visiting the Kantonian Gym at Malie City, Marowak was used in a battle against Ryuki and his Zweilous. However, Marowak was too distracted by Ryuki's rock and roll music and ended up losing the battle with direct hit from Zweilous' Dark Pulse.
When Mallow was working at Forest Pokémon Café to help Oranguru serve hungry Pokémon, Marowak and Turtonator both helped Kiawe as an extra chef in Aina's Kitchen. Due to the countless customers who had come to dine, all three of them were worn out as a result when Mallow returned. Also, Marowak and Turtonator with their friends were all excited that their Trainers all have Z-Rings. At Lillie's Mansion, Marowak and his friends were training for Alola League.
During the Alola League, Marowak was used to battle against Greedy Rapooh, and won, which allow Kiawe to move to the Quarter-Finals. Marowak was then used in the Semi-Finals to battle against Gladion's Lycanroc but lost along with Turtonator, which cause Kaiwe to Lose the League.
- Out of all the Pokémon caught by Ash and his friends after the start of the Sun & Moon series, Marowak is the only one to have been caught in a location other than Melemele Island.
- ^ SM034: A Crowning Moment of Truth!
- ^ SM035: Currying Favor and Flavor!
- ^ SM042: Alola, Kanto!
- ^ SM043: When Regions Collide!
- ^ SM053: Rescuing the Unwilling!
- ^ SM054: 10,000,000 Reasons to Fight!
- ^ SM055: The Professors' New Adventure!
- ^ SM061: A Mission of Ultra Urgency!
- ^ SM069: Rise and Shine, Starship!
- ^ SM078: Twirling with a Bang!
- ^ SM085: The Long Vault Home!
- ^ SM067: Love at First Twirl!
- ^ SM063: Pushing the Fiery Envelope!
- ^ SM070: The Young Flame Strikes Back!
- ^ SM087: Filling the Light with Darkness!
- ^ SM089: The Prism Between Light and Darkness!
- ^ SM090: Securing the Future!
- ^ Where Are You Going, Eevee?
- ^ SM107: Run, Heroes, Run!
- ^ SM118: Aiming for the Top Floor!
- ^ SM121: A Recipe for Success!
- ^ SM127: Chasing Memories, Creating Dreams!
- ^ SM131: The Battlefield of Truth and Love!
- ^ SM135: The Final Four!