The Battle Park owner's Blastoise is a water-type Pokémon owned by the Battle Park owner.
When the Battle Park's owner left to get supplies, Team Rocket took Charizard, Venusaur and Blastoise, challenging Ash to three battles. Jessie used Blastoise against Ash's Pikachu, which was a tough battle. Pikachu used Thunder to defeat Blastoise, but this was a distraction, as Pikachu was soon caught. Team Rocket used those Pokémon once more, but the Pokémon blasted them off, recognizing the Battle Park owner as their true owner.