In the Pokémon TV series, Ash’s Krabby evolves into Kingler during the Indigo League.
Ash catches Krabby before the Indigo Plateau Conference, but Professor Oak initially keeps it at his laboratory because Ash already has six Pokémon with him. Krabby later joins Ash for a conference match and evolves into Kingler during its first battle in the tournament.
The evolution is memorable because Kingler immediately demonstrates much greater strength than Krabby. It defeats three Pokémon in a row for Ash in the same Indigo League match, giving the previously overlooked Pokémon a dramatic showcase.
Kingler should not be confused with Ash’s later Water-type Pokémon. Cloyster, Gyarados, and Seaking are separate species that appear elsewhere in the anime. The evolution also follows the game relationship between Krabby and Kingler, although the anime presents it through an especially sudden tournament moment.