Grant's Onix first appeared when Grant was battling against Viola and her Surskit at the Battle Chateau. During the battle, Viola used the ice floor strategy she previously used in her Gym Battle against Ash. Unfortunately, Onix was able to withstand Surkit's attacks and trapped it with its Rock Tomb attack. Once it was trapped, Onix single handedly defeated Surskit with the combination of Rock Polish and Flash Cannon.
Onix was later used in the Gym Battle against Ash. It was the first Pokémon Grant used and it went up against Ash's Froakie. Onix tried to defeat Froakie, but somehow got confused with its Double Team. While trying to find the right one, it used Iron Tail and Rock Tomb. However, to Grant and Onix's surprise, Froakie used the tactic, the Rock Tomb Climb, to climb higher and Froakie finished Onix off with a direct hit with Water Pulse, thus winning the first match for Ash.