In Lillie's Egg-xhilarating Challenge!, Samson Oak revealed two Eggs to the students of the Pokémon School. While one Egg was received from his cousin from the Kantoregion, the other was found on Mount Lanakila. He decided to give the class an assignment to raise one of the Eggs and offered to let them choose between the two. Mallow suggested that Lillie should choose one of the Eggs and raise it, as it would potentially help her get over her inability to touch Pokémon. Lillie agreed and chose the one from Mount Lanakila, as she preferred it over the other one. She eventually named the Egg Snowy, a name it would retain once it hatched.
After class ended, Lillie and Ash traveled to Lillie's home in order to take care of the Egg. While they traveled, a wildSalandit managed to sneak onto Lillie's limousine in an attempt to attack the Egg. Later, when Lillie was alone in her room, the Salandit revealed itself and attacked the defenseless Egg. Despite her fear of Pokémon, Lillie instinctively shielded the Egg from harm, protecting it long enough for Ash and Hobbes to send Salandit flying. After Salandit ran away, Lillie realized that she had managed to touch the Egg without any trouble, but was still unable to touch regular Pokémon.
In Racing to a Big Event!, the Egg hatched into an AlolanVulpix. In the next episode, Samson Oak assigned the students to raise Snowy, and the students agreed that Lillie should keep it. Lillie caught Snowy despite her fear of Pokémon. On the day of its hatching, Lillie and Snowy spent much of the day bonding while walking in Hau'oli City. They went into a Malasada donut shop, where Lillie had Snowy try some different donuts. When they left the shop, they were challenged by Team Rocket. Snowy defended Lillie, first using Powder Snow to freeze a sidewalk to slow them down, then using Powder Snow to neutralize Mareanie's Sludge Bomb. When a second Sludge Bomb blew Snowy off a rooftop, Lillie jumped off after it and caught it. The two were saved by Ash's Rowlet with Leafage. Snowy then froze Team Rocket with Powder Snow, and they were taken away by Bewear. Lillie had no issue holding Snowy from that point on, though she was still afraid of other Pokémon.
In The Ol' Raise and Switch!, Professor Kukui tasked everyone with switching their partner Pokémon with somebody else and Snowy was given to Ash, whilst Pikachu went to Lillie. Snowy initially had trouble getting along with Ash, even refusing to eat the food offered to it. However, it eventually warmed up to him and agreed to do some battle training with him in order to surprise Lillie. When it came time to return the Pokémon to their proper owners, everybody was happy to learn that Lillie can now touch Pikachu after spending some time with him. As such, Ash decided to challenge Lillie to a battle, with him using Snowy against Lillie and Pikachu, to show how much stronger Snowy had become.
In Family Determination!, Snowy was used alongside Gladion's Silvally to battle a TotemKommo-o and several Jangmo-o and Hakamo-o. While Gladion fought Kommo-o, Snowy was able to fend off the Ally Pokémon with Powder Snow. It later froze the ground with Powder Snow, allowing Gladion to retrieve the Fairy Memory. This in turn allowed him to transform Silvally into a Fairy-type, enabling it to defeat Kommo-o.
In Rescuing the Unwilling!, Snowy joined Ash's Lycanroc against Lusamine's Clefable, which was under Nihilego's control. After Snowy knocked back Clefable with Powder Snow, Lillie reminded Clefable of the Clefairy doll they used to play with together, in order to free it from Nihilego's command. When Clefable began powering up a move, Lillie gestured Snowy and Lycanroc not to attack before freeing Clefable with a simple embrace.
In Getting a Jump on the Competition!, Ash and his classmates visited Mount Lanakila, where Snowy's Egg was found. Snowy ran off after sensing an AlolanNinetales nearby, which led Lillie to meet Cerah and her Ninetales during a PokéSled Jump. After watching their display, Lillie and Snowy decided to participate in the Pokémon Sled Jump Games and learn Aurora Veil. After some intense training, Snowy was finally able to successfully perform Aurora Veil during the competition, resulting in a successful jump. However, despite their impressive performance, Lillie and Snowy were unable to win.
In Not Caving Under Pressure!, Snowy and Lillie helped a group of AlolanSandshrew defeat a Tyranitar, which was trying to destroy their home. After emerging victorious, Sophocles gave Lillie an Ice Stone found by his Charjabug. Lillie asked Snowy if it wanted to use the stone to evolve, but Snowy got scared and refused to. As a result, Lillie decided to hold on to the stone in case Snowy ever changed its mind.
After Snowy first hatched, it was a very reserved Pokémon that didn't want to interact with anyone else but Lillie. When Ash tried to interact with it, it promptly froze him. Although it was newly hatched, it didn't hesitate to attack Team Rocket when they chased it, and it even froze them, despite Ash preparing to fight them himself with his Pikachu. By the end of Getting to Know You!, it warmed up to the Pokémon owned by its Trainer's friends and was willing to play with them. In The Ol' Raise and Switch!, it started to be more friendly and open towards other people after it had been with Ash over the weekend. It also started to develop a fondness for walks. Snowy has been supportive of its Trainer as seen in Night of a Thousand Poses! and Mission: Total Recall!, where after Lillie became scared of Pokémon again, Snowy remained near Lillie whilst keeping a distance until Lillie overcame her fear.
Snowy appears to be afraid of the change associated with evolving. In Not Caving Under Pressure!, Snowy witnessed a Pokémon evolve for the first time, reacting with a stunned silence. When Lillie asked if it would like to evolve as well, Snowy retreated from the Ice Stone and hid behind Mallow's Steenee.
A Japanese event distributed an in-game representation of Lillie's Alolan Vulpix, along with Mallow's Steenee and Kiawe's Turtonator via serial code and local wireless. The serial codes were available at Æon stores in Japan from July 5 to 14, 2017, and could be used until July 24, 2017. The local wireless were available at Pokémon Center stores and Pokémon Stores in Japan from July 22 to August 13, 2017.