In Splash, Dash, and Smash for the Crown!, Goh discovered that Magikarp had grown very fat over its time at the Cerise Laboratory. To fix this, Goh trained Magikarp to compete in the Magikarp High Jump Competition. During the tournament, Magikarp was able to make it to the semifinals, where it defeated Magikarpenter's Magikarp with a jump of 21.02 meters, breaking Goh's personal record in the process. In the finals, it competed against Kasukarp's Shiny Magikarp, Shinegoldie. Before the finals began, Magikarp was revealed to have had two immensely heavy weights on its back fin. With the weights gone, it jumped so high it didn't come back. As such, its jump could not be measured, losing Goh the tournament. At the end of the episode, it crashed back down on Ash and Goh while they were on Slowpoke Island.
As a giant Pokémon, Magikarp is exceptionally larger and stronger than other members of its infamously weak species. Its Splash, a normally useless move in its own right, allows it to jump so high it exits the atmosphere, and it can send opponents flying as it returns to the ground. Magikarp can be very motivated when it has a goal to strive towards.
Goh's Magikarp is very receptive to other Pokémon, welcoming Feeby and later Goh's newly captured Pyukumuku. However, it does not seem to like other Pokémon hanging from its back fin, as seen in Not Too Close for Comfort!.