Croagunk was first seen resting outside a supermarket in Gymbaliar!. When Meowth emerged from it, Croagunk followed him to where Team Rocket was using a fake Gym to steal unsuspecting Trainers' Pokémon. Their plan was going badly as it required Jessie to win, but her Dustox kept losing. As a result, she spotted Croagunk and decided to use it, subsequently winning many battles with it. After Ash and his friends entered the Gym, Croagunk lost against Ash's Aipom. Team Rocket resorted to grabbing Ash's Pikachu and running off, leaving Croagunk behind in the process. Brock was the first to notice Croagunk and felt a connection with him; Croagunk later willingly went into Brock's Poké Ball.
Croagunk was first used in a battle by Brock in Leave It To Brocko!, battling Seviper. The two had a brief clash of moves before Croagunk repeatedly used Brick Break while Seviper used Wrap on him, eventually ending in a draw.
Like Brock's Bonsly, Croagunk has attacked Brock in order to continue the anime's running gag of keeping Brock away from the girls who are the objects of his affection, to the point that even Croagunk's presence can be sensed by Brock, which may make Brock suddenly halt his romantic advances.
In All Dressed Up With Somewhere To Go!, Brock entered Croagunk in the Pokémon Dress-Up Contest, an event organized by the Pokémon Fan Club where Pokémon try to imitate other Pokémon. Throughout the competition, Croagunk replicated the behavior of a Politoed and his impression of the Frog Pokémon was so convincing that the panel of judges—formed by Mr. Sukizo, Nurse Joy, and Officer Jenny—deemed him the winner. As a result, Brock was given the Pokémon Egg prize.
In Glory Blaze!, Croagunk was briefly seen battling a Furret and a Hitmonchan alongside Holly's Nosepass in the second round of the Hearthome City Tag Battle Competition. Together they managed to defeat their opponents and advance their Trainers to the semifinal round. In Smells Like Team Spirit! he was used in the semi-finals, being paired off with Holly's Farfetch'd and was up against Ash's Staravia and Paul's Torterra. Paul showed total disregard for Ash, ordering Torterra to blast Farfetch'd with Hyper Beam, not caring that Staravia was hit as well. With Farfetch'd out, Croagunk challenged Torterra and managed to damage it with a powerful Brick Break to the head. Before Croagunk could follow up, Torterra recharged and hit Croagunk with Leaf Storm, winning the round single-handedly.
In Enter Galactic!, Croagunk protects Brock from a Dark Pulse launched by Saturn's Toxicroak. The two quickly gain a strong disliking of each other and begin fighting. The fight is ended prematurely when Saturn recalls Toxicroak so Team Galactic can escape.
In Cream of the Croagunk Crop!, Croagunk and Brock enter the Pastoria Croagunk Festival. Croagunk initially enters the stage and has his physical condition judged alongside the other Croagunk, with the judges becoming impressed with Brock's Croagunk. The next part has Croagunk go through a brick-breaking contest, with he does flawlessly, allowing him to challenge the former champion, Craig. The two take to the boxing ring and begin the match and Craig quickly lands a powerful Cross Chop and follows up with Dynamic Punch. Croagunk dodges and lands multiple Poison Jab attacks against Craig. The two seem evenly matched but are interrupted by Team Rocket. The two Croagunk, alongside the rest of the participants, attack the mecha, only to be trapped inside. However, Nurse Joy and her Croagunk, Chrissy, stop them with a Vacuum Wave. Chrissy's heroism led to the coronation of Nurse Joy and her Croagunk as champions of the festival, giving Brock's Croagunk an automatic disqualification.
In Losing Its Lustrous!, Brock begins flirting with a Nurse Joy, but after a few seconds feels that something is wrong and notices that Croagunk didn't stop him. He notices him instead staring out a window, causing Brock to worry over Croagunk's behavior. The reason is later revealed to be Croagunk sensing Saturn's Toxicroak with his Anticipation Ability. When it ends up getting close to Brock's location Croagunk releases himself from his Poké Ball and runs off to find it and start a battle. Later on Croagunk is seen falling through the skylight and lands hard on the ground. Toxicroak follows and hits Croagunk dead-on with a Poison Jab, knocking him out while Brock watches helplessly on from the roof.
In Battling a Cute Drama!, Brock met a Trainer named Marilyn and quickly became irritated by Marilyn's superficial attitude towards Pokémon. He decided to teach her about the inner strength and beauty of Pokémon with a battle and used Croagunk as his second Pokémon. Croagunk gains the upper hand against her Chingling, but it is just an act as Marilyn wanted to see Chingling take the attacks to make it more dramatic. Marilyn orders Chingling to use Growl along with Confusion and Croagunk is almost knocked out by the super effective move. Brock, not willing to give up, encourages Croagunk to keep going, and not wanting to let Brock down he does so and uses Brick Break, defeating Chingling.
In A Faux Oak Finish!, Croagunk guided the group through a marsh on the outskirts of Twinleaf Town. Using his skills, Croagunk was able to find safe spots for the group to walk on. Later, he encountered a wild Politoed and battled it.
In The Needs of the Three!, Croagunk once again battled with Saturn's Toxicroak. He quickly gets distracted and is hit by Sludge Bomb, so Brock recalls him. Later on the group attack Team Galactic again, with Croagunk leaping off of Gliscor to land a direct hit on the head with Brick Break to Toxicroak, knocking it out and giving Croagunk his first victory over it. He then assists in freeing the lake guardians and fighting Dialga and Palkia.
In BWS01, Croagunk once again halted Brock's romantic advances on Nurse Joy. Witnessing the dynamic between Brock and Croagunk, Cilan commented on their unique and spicy relationship.
Personality and characteristics
Croagunk showing off his behavior
Croagunk is very calm and collected and appears to be unaffected by some attacks (as seen when Seviper used Wrap on him). He has an excellent hearing ability as he could hear Buneary in the bush in Setting the World on its Buneary! and Team Rocket sneaking into Oreburgh Gym in O'er the Rampardos we Watched!, can sense things easily, and is depicted as being very intelligent. He is quite stealthy as he could leave a room without Brock even noticing that Croagunk left to find out what a noise was. Croagunk has been shown to have his own pace for things like eating, attacking, or following Brock. Similar to Ash's Treecko, he is also a bit of a loner, preferring to sit alone when eating or just resting. Although he is seen mostly angry or without any emotion, he was seen happy in Doc Brock!. Croagunk has been shown to be vain at times, once spending hours staring at his own reflection and having to be dragged away from it to help deal with Team Rocket.
Croagunk pulling Brock away after jabbing
He is a very powerful Pokémon, as demonstrated in his debut episode where he beat many Trainers while he was under Jessie's command. He has since become Brock's main battling Pokémon and has proved his power again and again, even stopping a Draco Meteor attack in The Rise of Darkrai. He has developed a rivalry with one of the other strength-oriented Pokémon on the cast, Ash's Buizel. He also has an extreme rivalry with Saturn's Toxicroak, to the point of actually ignoring Brock's advances on women.
Croagunk often attacks Brock to keep him away from the girls who are the objects of his affection, to the point that even Croagunk's presence can be sensed by Brock, which may make Brock suddenly halt his romantic advances. When forcefully dragging Brock away from girls, he usually uses Poison Jab, which makes Brock suddenly collapse so Croagunk can easily drag Brock away. However, when Brock pledged to save Oralie's Magikarp and Haley's Feebas in Ya See We Want An Evolution!, Croagunk still jabbed Brock, which caused Dawn to remark that Croagunk may have gone too far. Croagunk generally chuckles or laughs after attacking Brock, so it is possible that he actually enjoys it. However, Croagunk has also protected Brock from harm, such as falling off a bridge in Bibarel Gnaws Best! and from Saturn's Toxicroak's Dark Pulse attack in Enter Galactic!. According to the Pokétch in Not on MY Watch Ya Don't!, Croagunk is very close to Brock. In fact, Croagunk is about as close to Brock as Pikachu is to Ash, despite at the time having only been with him for two episodes, as opposed to Pikachu, which has been with Ash since the very first episode.
| Using Poison Sting
| A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.