Fergus is a Pokémon trainer who accepts Mewtwo's invitation to battle the world's greatest trainer on New Island. He proves his determination and capability as a trainer by successfully navigating the dangerous storm conjured by Mewtwo, becoming one of only four trainers—alongside Ash, Corey, and Neesha—to reach the island.

On New Island, Fergus participates in Mewtwo's challenge. He exclusively fields Pokémon renowned for their prowess in aquatic environments. While not all are strictly Water-types, each member of his team is an excellent swimmer. This team prominently features Gyarados, whose intimidating presence during an interaction visibly startles Misty.

In the battle against Mewtwo's cloned Pokémon, Fergus deploys his Gyarados. This confrontation forms a significant part of the initial clash between the invited trainers and Mewtwo's forces, standing as one of the few trainer battles depicted in detail against the clones.

The manga adaptation streamlines Fergus's role. It omits broader conflicts involving other trainers' Pokémon like Pikachu or Corey's Rhyhorn, making Fergus and his Gyarados the primary focus of the shortened pre-battle sequence against Mewtwo. This maintains his participation while narrowing the focus compared to the film.