By nature, Chespin is extremely gluttonous, especially when he comes across macarons, which is his favorite food to the extent that he would put himself in danger just to get them. He also tries to help people who are in danger, such as chasing after Team Rocket in order to save Professor Sycamore, Serena, and Bonnie. Chespin is also intelligent, as he was able to understand that the pieces of macaron that were left behind by Serena were markers, or was able to deduce that the cord he came across before was the power source for the "Mega Mega Mega Mecha Meowth" and thus tried to unplug it. Like Bunnelby, Chespin has a kind, friendly, and happy-go lucky personality, but isn't as mature as Bunnelby. In An Oasis of Hope, Chespin is also good on acting when he convinces Pikachu to act as being captured by Team Rocket while guarded by a rogue Grumpig and using its Vine Whip to serve as a lockpick to unlock the lock from the cage. He is also very determined to battle against Team Rocket and being teamed up with Ash's Pikachu to blasts them off with both of their Electro Ball and Pin Missile combination. In later episodes, Chespin also loves Serena's home made Poké Puffs as a replacement for his macarons.
At the start of Mega-Mega Meowth Madness, Ash and company discover Chespin at Professor Sycamore's Pokémon research lab when they notice that the macarons are missing, and one the employees named Sophie discovers and shows the group Chespin, who is hiding behind a plant, and eating the macarons. After telling off Chespin because of his behavior, Chespin jabs Clemont in his hand with one of the spikes on his head, before taking a handful of the macarons and running off, with Sophie explaining that Chespin enjoys macarons a bit too much, and is known for being a bit of a prankster.
He is also quite fond of Clemont after he saves him from getting hit which he also gives him some macarons and later he shares the macarons to Ash and the group including Professor Sycamore despite Clemont telling him to save some or there would be nothing left for him.
Chespin has a heated rivalry with Serena's Pancham when they first met due to the latter throws two twigs on his head and taunting him on purpose due to its mischievous behavior especially that he was the one responsible for instigating their fight. His rivalry with Pancham is similar to both Ash's Snivy and Iris' Emolga when they fight each other and showing their dislike with one another. Their heated rivalry is demonstrated in Pathways to Performance Partnering! after he ate most of Serena's Poké Puffs for everyone causing Pancham to get angry. They are usually seen arguing, fighting each other for small things and their bragging rights in who is the best. This also happens in the latest Pikachu's shorts where he bumps Pancham to be the best musical performer during the song performance while the latter does the same. Both are later seen headbutting at each other and running so fast while sticking each others' cheeks similar to both Ash's Pikachu and Raichu did in Pikachu's Vacation until they are bumped into a sleeping Snorlax.
In Love Strikes! Eevee, Yikes!, Both Chespin and Pancham gain a new rivalry towards a wild Quilladin which is Chespin's evolved form who is easily in love with Serena's Eevee until she rejects him at the same time to make him feel heartbroken as Serena tells him that Eevee is a little shy towards others.
Furthermore, Chespin is similar to Ash's Oshawott when it pops out of his Poké Ball and falling in love easily on other female Pokémon and at the same time he was left heartbroken when seeing female Pokémon comes across with another male Pokémon or both Pokémons are very close with one another. This trait is also shared by a wild Quilladin due to their evolutionary relation.
When Ash and his friends were visiting Professor Sycamore's lab and eating some of Serena's macaroons, Chespin stole some and began eating them himself. Clemont tries to make friends with him but ends up getting poked by Chespin's spikes. Chespin grabs the macaroons and ran away. However, after witnessing Professor Sycamore, Serena, and Bonnie getting captured by Team Rocket, Chespin decided to go and help Clemont and Ash rescue them, using the trail of macaroons that were left behind by Dedenne as markers. Once they found them, Chespin curiously went inside the hideout to try to find macaroons. But it ended up revealing itself to Team Rocket and accidentally caused them to know about Ash and Clemont's presence. When Team Rocket unleashed their Mega Mega Mega Mecha Meowth machine, Clemont pushed Chespin out of harm's way as it was about to get crushed. Afterwards, Clemont and Chespin started bonding for a bit. Chespin located the source of the power and assisted Clemont into pulling to plug in order to stop Team Rocket's machine. However, Team Rocket had a back-up generator and continued fighting. Chespin then assisted everyone into battling the machine, but to no avail. All of a sudden, a Mega Blaziken and it's trainer who is named Blaziken Mask arrived and weaken the machine with Flamethrower. This allowed Chespin and Pikachu to finish the battle and send Team Rocket flying. At the end of the day, Chespin asked Clemont to join him on his adventures, which he gladly accepted.
In one episode, Chespin becomes obese when he kept eating macarons but during the sparring match with Ash's Froakie, he is unable to move because of its weight. When Chespin lost, Clemont becomes worried for it until it was found by Carrie who owns a macarons bakeshop being challenged by Wylie who had a Delphox to beat him in a battle but it was called off.
Chespin is also used by Clemont when fighting against Team Rocket's Pokémon and also helps them climb on the mountain cliff.
Chespin is also fond of Serena's Poké Puffs as a replacement for his macarons which it was seen eating most of it until it reveals he was responsible when he also ate one of the Poké Puff for Fire-type Pokemon making Serena's Fennekin, Clemont's Bunnelby and Dedenne and Ash's Pikachu got mad from his gluttonous act.
Chespin later teams up with Ash's Pikachu and Serena's Fennekin against Tierno's Squirtle, Trevor's Charmander and Shauna's Bulbasaur during the last day of Summer Camp to battle for the hall of fame as Ash's team as Team Froakie won the battle with Pikachu's assistance.
Chespin is used again to fight against Team Rocket's Pokémon while teaming up with Ash's Froakie and Serena's Fennekin after the latter stops them from its tracks using its Frubbles due to their motives of stealing. Froakie distracts both Inkay and Pumpkaboo long enough and allowing both Chespin and Fennekin to blasts them off with both Flamethrower and Pin Missile combination.
In Splitting Heirs!, Chespin is in love with Heath's Meowstic due to its glamorous appearance. However, he becomes heartbroken soon when he finds out Meowstic likes Blake's Meowstic due to their close attachment as he tries his best to give flowers to it.
Chespin was watching Aria's Pokémon Showcase exhibition along with her Braixen until a Pancham crashing the show for its dance performance and showing its mischievous side. When Chespin practicing Aria's performance in the Pokémon Showcase, he got hit on his head by someone's twig after another until it reveals a Pancham who crashed the Pokémon Showcase performance was responsible taunting him making Chespin get angry to chase it. When Pancham was found taking a nap, Chespin angrily wants to fight while trying to wake it up by pulling its leaf on its mouth. Chespin later aids Ash's Pikachu to fight Team Rocket until they manage to blast them off.
It was used again while teaming up with Clemont's Luxio, Ash's Pikachu and Froakie and Serena's Fennekin by destroying a large boulder to make the wild Lapras pass through the river stream before being confronted by Team Rocket. 
This demonstrates both Chespin and Serena's Pancham's heated rivalry when he acts gluttonous to eat most of Serena's homemade Poké Puffs. Serena and Clemont do their best to stop them from fighting until Pancham angrily chases Chespin and accidentally tackles Nini's Farfetch'd while practicing with her Smoochum. When Nini decides to trade her Pokemon for Serena's Pancham. Chespin decides to be traded by her but since Serena refuses the trade it backfires causing the two to argue.
As Team Rocket captures them on purpose by being caught in a lavender rubber ball, both Chespin and Pancham are still fighting which causes everyone to get rolled inside the ball until it falls down and breaks. When Farfetch'd knows the way, both Chespin and Pancham are still arguing this is the right way as Serena's Fennekin pass them until James' Inkay found them. By the time Fennekin, Smoocham and Farfetch'd are down despite her efforts to defend them, Chespin and Pancham teams up to fight both Inkay and Jessie's Pumpkaboo with their powerful abilities as Ash and the group arrive in time to find them. Both eventually defeats the Team Rocket's Pokemon with both Pin Missile and Dark Pulse combination allowing Pikachu to blasts them off with its Thunderbolt. Despite teaming up each other, Chespin and Pancham are still fighting for small things which Ash remarks that their fighting each other is considered to make them as great friends.
Chespin is also seen making accident on Serena's Pancham during dinner night as both begins to argue. Chespin later teams up with Ash's Pikachu and Frogadier and Serena's Fennekin to blasts Team Rocket off with their powerful abilities. During the festival, Chespin is later seen having a picnic with all of Ash's Pokémon by eating fruits and berries given by Ash as their gift as he, Luxio and Bunnelby are shared by a single gift which is a music box that resembles them and it was invented by Clemont.
In A Showcase Debut!, Chespin was seen with Clemont, Bonnie, Ash and Pikachu watching Serena's first debut in the Pokémon Showcase only to be failed when her Fennekin got tripped from her ribbons when she follows Serena in the contest.
In An Oasis of Hope!, Chespin was released by itself when Pikachu is about to be locked up in the cage by Team Rocket due to their threat on attacking all the controlled Spoink using Grumpig and its abilities. As they were locked in the cage, Chespin uses its Vine Whip to unlock the lock similar to a lockpick which its successfully do it after Goomy who is now evolved into Sliggoo blasts Grumpig off to the sky with its newly learned Dragon Breath and frees all of the Spoink from its Psychic grip. Chespin was seen with Sliggoo and Frogadier watch all of the Spoink are mad at Grumpig who is later betrayed and used by Team Rocket for their evil scheme which it apologizes for his horrible actions until one of the Spoink who accepts its apology by giving it some apple much to Grumpig's happiness.
In Confronting the Darkness!, Chespin finally reunites with Ash's Pikachu when Ash, Serena and Bonnie arrived at Lumiose City to reunite with Clemont.
In The Moment of the Lumiose Truth!, Chespin joins up with Dedenne and both Serena's Braixen and Pancham to watch and cheer the Gym battle between Ash and Clemont.
In Beyond the Rainbow!, Chespin teams up with Serena's Braixen to hold off a group of Pinsir and a Ariados to make Ash, Pikachu and Goodra to proceed to find Florges and her group of Seviper.
Chespin is seen chasing his rival Serena's Pancham until they are spotted by Team Rocket. After the three Pangoro attacked them with their abilities to make them separated, Chespin is with Serena and Ash's Frogadier. He and Frogadier serve as brief bodyguards as he encountered one of the three Pangoro much to his horror as Frogadier manage to blind its eye using its frubbles to escape. They finally reunite with Ash, Hawlucha, Fletchinder, Pancham and Clemont's Luxray and later Clemont, Pikachu and Serena's Braixen. Chespin also saw his rival Pancham finally spoke with the three Pangoro due to its evolutionary relation and realizing their food supplies such as apples are stolen by thieves which Meowth realizes their occupation and their motives of stealing until the arrival of Jessie, James and Wobbuffet. After the three Pangoro blasts Team Rocket off with their abilities, they apologizes to Ash and the group for the misunderstanding as they also gave apples as part of their apology to which everyone is happy.
In Scary Hospitality!, Chespin released by itself to eat with Pikachu and Dedenne. Chespin also reveals to be afraid when Lon was telling scary stories and his Gastly and its evolutionary stages, Haunter and Gengar are causing mischief inside the scary mansion especially when Ash, Bonnie and Serena are trapped in the basement after falling into a trap door. Chespin is always clinging on Clemont's leg due to being afraid.
In A Festival Trade! A Festival Farewell!, Chespin wears a Pikachu costume for the Gourgeist Festival until being caught by the count's butler and all of his Gourgeist thinking it was a Pikachu. After Jessie trades it back with Count Pumpka's Mawile to retrieve her Pumpkaboo back who is now evolved into a Gourgeist. Ash and the group manage to confront them which happens to be Team Rocket. Clemont's Bunnelby manage to knock Inkay into the glass to free Chespin inside and were blasted off from Ash's Pikachu's Thunderbolt and Serena's Braixen's Flamethrower.
Chespin was seen with Pikachu guarding a wild Snover who has a fever along with a wild Abomasnow when Ash and the others are getting the Spring Moss and the Yellow Marigold. Later when Team Rocket captures Abomasnow, Chespin was used to fight James' Inkay by hitting with its Pin Missile to distract them then using its Vine Whip to lift and throw Serena's Braixen to release Abomasnow from the net using Scratch.
In Adventures of Running Errands!, Chespin teams up with Clemont's Bunnelby are given errands by Clemont to find the short fuse. His gluttonous nature, his mischievous side and its romantic behavior are prevented by Bunnelby by dragging away even chasing a wild Fearow to get the purse and to outsmart it and both of them are losing their way. Upon reaching the house on top of the hill, they were blocked by Team Rocket as both tried to fight both James' Inkay and Jessie's Gourgeist until they were rescued by Ash's Fletchinder who uses Steel Wing to deflect Gourgeist's Shadow Ball. When Ash attempted to release both Frogadier and Hawlucha, Bunnelby hits Team Rocket with Mud Shot on their faces as Chespin blasts them away with Pin Missile. After the errand and getting the fuse, Clemont finally fixed the power transformer as the powers in the Pokemon Center have finally have power back on. As everyone are eating Pokemon food, Chespin ends up getting overeating most of it causing him to hurt its stomach making him as first patient for Nurse Joy while being assisted by Clemont.
Chespin teams up with Clemont, Luxray and Bunnelby to find the wild Eevee. They use one Poke Puff as baot which Chespin wants to get the puff but was stop by Clemont who scold it. As Bunnelby let Eevee take the Poke Puff without noticing, Chespin almost caught Eevee but he was blamed by Clemont and Luxray. After Serena caught Eevee and released to meet all of the group's Pokemon, Eevee was afraid and hides on Bunnelby due to her shyness as Chespin wants to make friends with as he chases Eevee in circles to make Bunnelby dizzy.
Chespin is the only Pokemon can scare Eevee because of his mischievous behavior even trying to practice in how to get along with other Pokemon to make Eevee scared and hides on Serena much to his disappointment. Chespin cheers along with Bunnelby, Frogadier, Braixen and Pancham when both Ash's Pikachu and Tierno's Blastoise face both Serena's Eevee and Shauna's Ivysaur in a tag battle.
In Love Strikes! Eevee, Yikes!, Chespin and Pancham gain a rivalry towards a wild Quilladin and like Chespin because of their evolutionary relation, he is easily in love with Serena's Eevee. Chespin later fights Quilladin after his rival Pancham, it manages to dodge all of Chespin's attacks but was hit from its Rollout. As both continued to fight, Eevee, Bunnelby, Squishy and Dedenne are captured by Team Rocket. After they escape and both Dedenne and Bunnelby defend both Eevee and Squishy, Chespin, Quilladin and Pancham teams up to stop them which Quilladin makes a truce for them. Pancham knocks Jessie's Gourgeist with Hammer Arm while Chespin knocks James' Inkay with Pin Missile to knock both James and Jessie down allowing Quilladin to blasts them off with Rollout. After Quilladin is rejected by Eevee and Serena explains it about her shyness, Chespin cheers him up before it was easily in love with a wild Flareon and both Chespin and Pancham watch it go.
Chespin was released to help the wild Litleo by covering its vines together using Vine Whip to make him block from washing away from a running current allowing it to make it cross the land. Clemont was amazed to Chespin's efforts which he shows his coolness.
As everyone is asleep when Darkrai enters their dreams, Chespin appears along his rival Serena's Pancham in Pikachu, Meowth and Squishy's dream. As they argue, both evolves into Pangoro and Chesnaught which is Chespin's final evolved form rather than evolving into Quilladin before evolving from its full form and Pikachu tries to stop them from arguing. Both Pancham and Chespin are still dreaming from their sleep as both from their evolved forms in their dreams are seen fighting each other.
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- Chespin is the only regional Grass-type starter Pokémon to be owned by a main character other than Ash.
- Chespin has the tendency to pop out of its Poké Ball without being called on, a trait shared by Misty's Psyduck, Jessie's Wobbuffet, May's Skitty and Munchlax and Ash's Oshawott.
- Chespin is Clemont's only Pokémon that doesn't know any Electric-type moves.
- Chespin has an obsession with food, similar to Ash's Snorlax, May's Munchlax, Dawn's Mamoswine and Iris' Emolga.
- ^ XY109: Master Class Choices!; the Attract from Amelia's Dragonair and Espeon caused him to fall in love with them.
- ^ XY010: Mega-Mega Meowth Madness!
- ^ XY015: An Appetite for Battle!
- ^ XY046: Dreaming a Performer's Dream!
- ^ XY048: Bonnie for the Defense!
- ^ a b XY049: Pathways to Performance Partnering!
- ^ XY098: Dream a Little Dream from Me!