As a Squirtle, being picked to be Tierno's first Pokémon
Blastoise debuted as a Squirtle in Summer of Discovery!, where he was first seen battling a Trainer's Conkeldurr. He easily managed to outmaneuver the Muscular Pokémon with his dance techniques and defeated it with Skull Bash. Squirtle later participated in a first-touch battle against Ash's Froakie and won.
In Tag Team Battle Inspiration!, Wartortle was revealed to have evolved into a Blastoise. He participated in a Tag Battle along with Ash's Pikachu against Shauna's Ivysaur and Serena's Eevee, in an attempt to get the latter Pokémon to overcome its shyness. Blastoise's dancing inspired Eevee to respond with her own dancing, allowing her to evade Blastoise's attacks and land a hit with Swift until Serena called the battle off in order to practice for her upcoming Pokémon Showcase.
After that, Blastoise went up against Sawyer's Sceptile. He managed to stand his ground for a while, even resisting a super effective Leaf Blade, but ended up losing after he got hit by Frenzy Plant. Before he fainted, he used Rain Dance to change the weather and make things easier for his teammate Raichu.
He is a friendly Pokémon that often dances with his Trainer, but can be annoyed if attacked, as shown when Raichu accidentally hit him with Thunderbolt. As a Squirtle, he used his nimble dance moves to outmaneuver his opponents in battle, allowing him to defeat much larger and imposing Pokémon such as Conkeldurr, and giving him an upper hand over Ash's Froakie. He maintained his agility even after evolving into the much more bulky Blastoise.
Blastoise is very loyal to Tierno and shares some personality traits with his Trainer. He is a skillful dancer and he is able to easily mimic Tierno's dance moves.