Gastrodon was used to battle Ash's Staraptor in the Sinnoh League's semi-finals. It used Muddy Water, but was countered by Staraptor's Quick Attack. However, it copied Ash's counter shield tactic with Muddy Water, and swatted Staraptor away with ease. When Staraptor found an opening, Gastrodon used Body Slam before Staraptor could land a hit, and crushed it. It launched Water Pulse up, and planned to jump out of the way at the last second. Staraptor used Close Combat on the ground to escape, but Gastrodon stroke him down immediately with Ice Beam. In that moment, Ash's Buizel came out before Gastrodon could finish Staraptor. Buizel used Aqua Jet against Ice Beam to make Ice Aqua Jet, then used Ice Punch to finish Gastrodon.
To mark its defeat in the battle, Gastrodon's picture was blackened out on the scoreboard.