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 Kanto region, the other was found on Mount Lanakila. He decided to give the class an assignment to raise one of the Eggs and offers 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 would eventually name 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 wild Salandit 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 had 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 Alolan Vulpix. 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 gotten.
In SM043, Lillie used Snowy alongside Togedemaru in a battle against Brock's Geodude. Geodude took no damage from Togedemaru's Zing Zap and knocked away Snowy's Powder Snow with a Gyro Ball Counter Shield.
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 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.
Snowy has also been shown to take initiative, in order to help, even when its assistance isn't needed. For example, in Lulled to La-La Land!, Snowy blew a cold breath of air on a fire that had been created by Litten to cook a pot of curry; the breath ended up freezing the curry. This was also demonstrated in SM041, when Ash, Kiawe, and Sophocles were only on fire due to their excitement for the upcoming Charjabug Race. In the Poké Problem segment for The Ol' Raise and Switch!, Snowy was also shown to have picked up some of Ash's habits, like his way of eating, as demonstrated when the Fox Pokémon quickly ate up the food Lillie gave to it.
Snowy seems to get motion sickness while on a plane, as shown in SM042.