Serperior is Monta's starter Pokémon that he first obtained as a Snivy. Serperior is Monta's most powerful Pokémon and is also his best friend. It was used in its first battle against a wild Patrat. It is then used in a Double Battle against a wild Patrat and Watchog. He ordered a Tackle on the Watchog, but just when he is about to capture it, Bianca and Cheren appear.
Later, Monta uses it in a Double Battle with Cheren's Tepig against a Bike Gang King's Braviary. It starts off with a Vine Whip, which does hardly any damage. Braviary uses Wing Attack, hurting it badly. It is nearly taken out by a Fury Attack, but Monta gives it an Oran Berry to revive it and goes in with a Grass Pledge, with Fire Pledge creating the combination needed to defeat Braviary.
Snivy was used in a battle against Cheren's Tepig, Pansage, and Basculin with Panpour and Roggenrola. Snivy started off with a Leaf Tornado, which died down before it could reach the Pokémon and instead was hurt by Tepig's Ember. It attacked Basculin with a Vine Whip, but it switched with Tepig. After Panpour uses Surf and defeats Tepig, he had not noticed that Snivy has fainted too.
Snivy is used to battle an Emolga. He weakened it with Leaf Tornado before he caught it. Later, the group entered a cave and suddenly the ground starts to rumble and a wild Excadrill appears and battles Snivy. Using some impressive moves, he is able to catch it.
It is then used in a battle against a Pokémon Ranger's Zebstrika and Swanna with Emolga. It is hurt badly by Swanna's Aerial Ace, which made Monta switch Snivy out for his newly caught Excadrill.
Snivy was sent out along with Monta's newly evolved Boldore during a challenge in the Battle Subway. Thanks to the Air Balloon that it was holding, Snivy did not take any damage from Ground-type moves.
Snivy evolved into a Servine and was used to battle some wild Pokémon. It took on a Tornadus that Monta wanted to capture but Tornadus kept on fleeing.
Servine evolved into a Serperior sometime before the events of encountering Kyurem in Pokédex Complete!. Serperior was the first Pokémon to battle Kyurem but despite putting up a fight, Serperior stood no match for Kyurem.
Serperior was used along Victini in a Double Battle against Muteki's Jellicent and Hydreigon. In the first match, Serperior got beaten sometime after Victini used V-create. During the rematch, Serperior did much better.
Serperior was lent to Cheren during his Triple Battle against Monta's Victini, Reshiram and Zekrom. Serperior was reluctant at first to fight its best friend but decided to do so after Monta convinced it. During the battle, it was taken out by Monta's Reshiram. After the battle, Serperior's feelings were hurt and Monta tried comforting it. When Monta hugged Serperior, Serperior did the same but squished him in happiness.