Horsea first appeared in Tentacool & Tentacruel. Ash and his friends had missed their ferry service back to the Kanto mainland when they spotted the injured Horsea near the coast at Porta Vista. It squirted out a warning in ink that Ash and his friends didn't initially understand. The got Horsea healed, giving it a Super Potion. Later, the group learned that a woman named Nastina was trying to build an underwater resort in the local reefs, and that her workers were being attacked by many Tentacool. A strange chain of events lead to Porta Vista being attacked by a gigantic Tentacruel and a swarm of Tentacool, who was angry at the humans destroying the reef. Horsea and Misty's pleading saved the city, and Horsea then joined Misty's team.
Horsea next appeared in The Battling Eevee Brothers, where it swam in a fountain at the Eevee brothersEvolution party. The guests’ Pokémon including Horsea were captured by Team Rocket. Using its ability to spray ink, Horsea left a trail on the ground, allowing Ash and the others to quickly locate the Rocket trio. Horsea later sprayed ink at Jessie to distract her, helping Mikey recover his stolen Eevee.
Much later, in The Misty Mermaid, Horsea was feeling ill because Misty wasn't letting it out enough to get any exercise. With no ocean nearby, Misty decided to take it home, where it could play and swim in the Cerulean Gym's many aquariums. When she arrived home, Misty was roped into her sisters' underwater ballet performance as the lead mermaid. Horsea also took part, playing the role of one of Misty’s underwater friends. Team Rocket later gate crashed the show. Misty tried to take on Jessie's Arbok, though its Bubble attack was swatted away. Arbok attempted to Wrap itself around Horsea, but Horsea used a Smokescreen to escape and the other Pokemon took out Team Rocket. After the show, Misty reluctantly left Horsea and her Starmie in the care of her sisters.
As shown in its debut, Horsea prefers to use words before battling head on. Horsea, like Goldeen, had trouble functioning on land, so Misty didn't use it much in her battles. Misty was particularly protective of Horsea and she would normally carry it, namely because of its small size. However, when it was used, it proved to be very resourceful - using ink to draw pictures or leave trails. It, like the rest of its species, prefers large bodies of water to swim in, hence, it grew sad and ill when it was forced to swim in small puddles of water, and Misty later left it at the Cerulean Gym, so that it could swim to its heart's content in the Gym's pool.
Misty's Horsea appeared in Cerulean City where it was seen in her Gym.
In the TCG
Horsea was featured in the TCG as one of Misty's Pokémon. The following is a list of cards named Misty's Horsea.
Misty's Horsea Cards listed with a blue background are only legal to use in the current Expanded format. Cards listed with a silver background are legal to use in both the current Standard and Expanded formats.