Corey is one of four Pokémon Trainers who managed to brave Mewtwo's storm to get to New Island by riding his Pidgeot.
Corey battled Mewtwo's clone Venusaur using his own Venusaur called Bruteroot. The battle ended quickly after Mewtwo's Venusaur used Vine Whip to deflect Bruteroot's Razor Leaf and then used its Vine Whip to throw Bruteroot.