Ash captured Kingler as a Krabby in "TB013: Mystery at the Lighthouse" to prove to Misty that he caught his other Pokémon genuinely. Immediately after the capture, Krabby's Poké Ball teleported away, both surprising and upsetting Ash. The reason behind why the Poké Ball teleported away is because Ash already has six Pokémon in his team. Brock later explained that Krabby was sent to Professor Oak.
In "TB077: Round One—Begin!," Ash decided to use Krabby in the first round of the Pokémon League, reasoning that it would be perfect on a Water battle field, despite the fact that Krabby had never battled before. Despite the type disadvantage, Krabby managed to defeat Mandi's Exeggutor and the experience it subsequently gained during the battle caused it to evolve into a Kingler.
Kingler then went on to defeat Mandi's Seadra and Golbat all by itself, winning the match for Ash. Kingler was also used on the Ice field, where it defeated Pete Pebbleman's Cloyster, before losing against his Arcanine.
Kingler was planned to be used in the Silver Conference, but was injured before the match. Because of this, Ash was forced to use his Squirtle instead.
