Advanced Generation series
Glalie was first seen in Let it Snow, Let it Snow, Let it Snorunt!, on Izabe Island as a Snorunt. It followed Ash and the gang through the snow to the Pokémon Center, where it began to cause trouble and stole Ash's Badge case. Once Ash, Pikachu and Corphish cornered it, Snorunt froze Ash's Stone Badge, threw it into the air and escaped with the rest of the Badges using Double Team. Snorunt then started dropping the Badges one by one to make its "game" more interesting. After a small meeting with Team Rocket, it froze Ash with Icy Wind and left the Center through the window into an oncoming snowstorm. Ash follows it and they end up lost in the snow. After Ash got knocked unconscious by protecting it from a small avalanche, Snorunt took him to a cave, safe from the blizzard. After Ash awakes, Snorunt hands him some apples and while Ash begins to trust the mischievous Pokémon, Snorunt runs off into the blizzard with his hat. It takes the hat back to the Pokémon Center and then leads the gang to where Ash is. Reunited, the gang scold Snorunt and ask for the other Badges; however they are interrupted by Team Rocket when they capture Snorunt and Pikachu. Snorunt quickly escaped and saved Pikachu, before battling Team Rocket's Pokémon. Later on, Snorunt still refused to return the Badge case, so Ash battled it and subsequently caught it. It was introduced to the gang's other Pokémon at the end of the episode where it continued to prank everyone.
In the next episode, Do I Hear a Ralts?, Snorunt joined Max in his effort to get an unwell Ralts to a Pokémon Center.
In The Great Eight Fate! Ash chose Snorunt as well as his Pikachu as his first two Pokémon in a Double Battle in the first round of the Sootopolis Gym battle; they went up against Juan's Sealeo and Seaking. Pikachu used his Thunderbolt on Sealeo but Seaking used Horn Drill to reflect it back to Snorunt. Pikachu then used Thunder, but Seaking used Horn Drill against to reflect the attack to Snorunt again but this time Pikachu protected Snorunt taking most of the damage. Sealeo then used Blizzard on the two, Pikachu took a lot of damage but Snorunt barely felt the attack being part Ice-type and jumped around happily. Snorunt then used its Icy Wind to stop the Blizzard creating an Ice Pillar blocking everyone's view but Sealeo and Seaking destroyed it with their Aurora Beam and Hyper Beam respectively, this created ice shards which Ash had Snorunt and Pikachu jump on, Snorunt used Headbutt whilst Pikachu used Iron Tail, Seaking then used Hyper Beam on Snorunt and Sealeo used Aurora Beam on Pikachu, whilst Pikachu was able to dodge the attack, Snorunt wasn't and the Hyper Beam knocked it out.
In Date Expectations!, Ash began trying to teach it Ice Beam. While learning the new move, Snorunt ended up freezing people multiple times, including its Trainer and Anthony. Finally in Rhapsody in Drew, Robert gave it some words of advice on how to focus the attack while battling Team Rocket during the Grand Festival, Snorunt then evolves into Glalie and sends them blasting off with its newly mastered Ice Beam.
Glalie had several battles in the Ever Grande Conference and proved to be quite a powerhouse in Ash's team. In Shocks and Bonds, it teamed up with Grovyle to battle Clark and his Pokémon, Quilava and Charizard. Glalie's Icy Wind did not damage either Pokémon but managed to hold off Heat Wave. Grovyle and Quilava both went down, leaving Glalie against Charizard. Glalie froze up part of the battlefield so it could avoid Charizard's Flamethrower, but ended up being knocked around its own ice pillars. Glalie managed to change this to its advantage, using the momentum to raise its speed and used a high speed Headbutt to flatten Charizard and give Ash the win.
Ash used Glalie as his third Pokémon in his Full Battle against Katie. It went up against her Dugtrio, Dugtrio used Dig but Glalie used Headbutt on the ground forcing Dugtrio to emerge and dealing damage, Glalie then used Ice Beam, knocking Dugtrio out. Glalie then went up against her Misdreavus, Glalie used Ice Beam but Katie had Misdreavus take the attack, Glalie then used Headbutt, whilst being hit, Misdreavus used Destiny Bond, the Headbutt then defeated Misdreavus, but due to the effect of Destiny Bond, Glalie was also knocked out.
In Choose It or Lose It!, Ash used Glalie as his sixth and final Pokémon in his Full Battle against Morrison, it went up against his final Pokémon, his Metang who had the type advantage. Glalie used Headbutt whilst Metang used Take Down, with Take Down dealing more damage, Glalie used Ice Beam, which Metang was able to redirect with Confusion hitting Glalie. It was then hit with Take Down. Glalie used Ice Beam and Metang reflected it with Confusion again, but Ash saw this coming and used Icy Wind to redirect the attack back to Metang again, hitting it. Glalie hit Metang with Headbutt, but Metang countered with a super-effective Meteor Mash. Glalie used Headbutt, spinning to increase its power, whilst Metang used Meteor Mash. Just before the collision Glalie ducked, avoiding the Meteor Mash and hitting the spinning Headbutt, knocking out Metang, winning Ash the battle and moving Ash to the next round of the Victory Tournament.
Later, Ash used Glalie as his first Pokémon in his Full Battle against Tyson. It went up against his Sceptile, Glalie used Ice Beam whilst Sceptile used Solar Beam creating a massive explosion. In the next episode, it was revealed that this explosion knocked out both Pokémon.
In The Right Place and the Right Mime, Ash left Glalie at Prof. Oak's laboratory, before he went to challenge the Battle Frontier.
Diamond & Pearl series
He returned to Ash’s team in An Old Family Blend! for the Lily of the Valley Conference. Upon seeing his Trainer, it froze Ash with Ice Beam, which Torkoal later thawed him out. In Working on a Right Move!, Glalie was seen training with Torterra and Infernape before Ash’s battle with Conway. Ash was initially going to use his Glalie because of its power, to try to overwhelm Conway, but changed his mind as he knew that he couldn't depend on sheer power alone. In the end, Glalie was not seen participating in the Lily of the Valley Conference.
Best Wishes series
Glalie was reunited with Ash in The Dream Continues!, where he and the rest of Ash's Pokémon posed in a group photo with him.