Stunfisk was first seen inhabiting a lake with its friend Palpitoad and a group of Tympole in Facing Fear with Eyes Wide Open!. Palpitoad asked for Stunfisk's help to get rid of Ash and Oshawott as it viewed them as intruders. Stunfisk managed to get them out of the lake and planned to guard against them, but Cilan used his fishing skills with his special lure to catch and pull Stunfisk to shore. Palpitoad then appeared before the group and had Stunfisk fire Mud Bomb at the Pokémon Connoisseur but he managed to evade it. Cilan then lifted his fishing rod in the air and started to spin Stunfisk around, keeping it at bay until Ash was able to defeat Palpitoad. Once he did, Cilan dropped the Trap Pokémon to the ground which, with the combination of dizziness, knocked it out and Cilan captured it.
In Cilan Takes Flight!, Cilan called upon Stunfisk to participate in Skyla's "Air Battle" simulation, during which she predicted that Stunfisk would be defeated by her Swoobat. However, by the time Stunfisk was sent out to battle her, Swoobat had already been defeated by Crustle. Stunfisk was sent out to fight Skyla's Swanna after Crustle was defeated. Despite Thunder Shock being extremely effective against Swanna, it was still able to throw Stunfisk off momentum and into the air with Hurricane. Cilan had Stunfisk take advantage of its situation and use Scald while spinning, showering Swanna in hot water, which burnt it. Stunfisk was then defeated after Swanna used Aqua Ring to heal the burn and hit it with Brave Bird.
Stunfisk was called out in To Catch a Rotom! by Cilan to find out how its Thunder Shock attack would taste to a trio of Rotom. Much to Stunfisk's embarrassment, the Plasma Pokémon disliked the electricity it produced. When Team Rocket began their plan to capture the Rotom by feeding them electricity, Stunfisk volunteered to help by feeding them its own, but was shot down by Cilan. However, Stunfisk managed to rescue the Rotom alongside Krookodile and Excadrill by shielding them from the electricity, absorbing it as a Ground-type.
In BWS01, Stunfisk helped Ayumi perfect her partner Pikachu's Thunderbolt. After a few attempts, they finally landed a hit on Stunfisk, who giddily enjoyed absorbing the electricity. Stunfisk was later seen playing with Pikachu while Cilan, Brock, and Ayumi ate lunch.
In its debut, Stunfisk was quite aggressive, like the other Pokémon living in the lake. However strong Stunfisk was, it still obeyed Palpitoad, proving it doesn't function well in a group without being a 'follower'. After Cilan caught Stunfisk, its personality did not change; as shown in Archeops In The Modern World! where after being brought out by Emolga's Volt Switch it attacked a newly revived curious Archen with a Thunder Shock attack when Archen bit it and subsequently laughed. However, it seems to have completely accepted Cilan as its Trainer, and new leader figure. In Crisis at Chargestone Cave!, Stunfisk did not show any aggression towards the other Pokémon, even smiling as it watched Oshawott flirt with Emolga, showing that it is satisfied with its group. Stunfisk also dislikes being stepped on, and cries whenever it happens as seen in The Lonely Deino! and To Catch a Rotom!.