He first appeared in the Astilbe Town Battle Club pass Twist Mountain battling a trainer with a Mienshao and Watchog in a double battle, easily winning with his impressive combos with his Fire Warrior team: Emboar and Heatmor. After winning, he proceeded to pick on the loser to let him see their Pokémon and take the "good" ones from anyone without potential, infuriating Ash and company. They confronted him to stop all this, but Shamus simply forgets about getting his hands on people's Pokémon and brushes off the conversation since Don George comes by, then walks off.
Later on, Tepig ran up to him while he was eating, seemingly knowing him. It was then that he revealed that he abandoned Tepig in the Accumula Town Battle Club after it lost, believing that Tepig was weak. To prove his point, he challenged Ash to a double battle against Ash's Snivy and Tepig.
The next day, shortly after beginning the battle, he reveals to Tepig that he was feigning caring about Tepig and could care less about it and then looks for another Tepig that has less talent than it was in order to replace him. All he could care about is "power". Shamus held the upper hand in the battle as Heatmor erased the effects of Attract on Emboar with Fury Swipes and managed to knock out Snivy with a combo move of Fire Spin and Flare Blitz. Tepig held on just long enough to regain its confidence and evolve into Pignite. Using its powerful new Fire Pledge and Flame Charge as a combo, Emboar and Heatmor were defeated, surprising Shamus. Afterwards, he offered to take Pignite back as a result of losing to Ash, commenting on its power to use to make him his new Fire Warrior member. Pignite simply answered him with a Flamethrower to his head with a word meaning no because he liked Ash better than him, in which it was an outrage to him and he ran away hoping that Ash would regret keeping Pignite.
Emboar was first seen along with Heatmor when Shamus was double battling a trainer that owned a Watchog and a Mienshao. The two were able to defeat the Normal and Fighting-types. It was then used against Ash's Snivy and Tepig, but fainted when Ash's Tepig evolved into Pignite and used a Fire Pledge/Flame Charge combo.
Heatmor was first seen along with Emboar when Shamus was double battling a trainer that owned a Watchog and a Mienshao. The two were able to defeat the Normal and Fighting-types. It was then used against Ash's Snivy and Tepig, but fainted when Ash's Tepig evolved into Pignite and used a Fire Pledge/Flame Charge combo.