Roark sent Onix, who countered Elekid with Slam, but was stopped by its Protect. However, Onix dealt a lot of damage with Double-Edge, without sustating recoil damage, due to Rock Head Ability. Next, Onix deployed Stealth Rock, before using Slam to wound Elekid. Onix became paralyzed, due to Elekid's Static ability, and the two sides clashed with Brick Break and Double-Edge attacks. Paul then recalled Elekid and sent Chimchar, who faced Onix. Onix went to use another Double-Edge, but Chimchar used Dig, which proved effective. Using another Dig, Chimchar defeated Onix. Onix appeared again when Roark battled Ash, when his Cranidos was defeated. Onix easily defeated Turtwig with a single Double-Edge. Onix then battled Pikachu, who used Iron Tail against its Slam. Pikachu then used Thunderbolt, to change the rocks so Onix could not execute Double-Edge attack. As Pikachu went to use Quick Attack, Onix won by unleashing a Screech, blowing Pikachu into a rock, defeating him and winning the battle.
When Ash and Roark encountered each other, they remembered Paul and his Pokémon in the Gym Battle against Roark's Pokémon (including Onix). Roark reminded Ash that he should be training to win the Gym Battle, instead of letting Paul get to him. Onix battled Pikachu a second time during Ash and Roark's rematch. Pikachu started off with Quick Attack, avoiding Onix's Slam attack, and going atop of its head to prevent being affected by Screech. Onix attempted to shake Pikachu off, but got wounded by its Iron Tail. As Onix moved to use Double-Edge, Pikachu spinned around to use Iron Tail, but failed. Pikachu used a Thunderbolt that was powerful enough to actually hurt Onix, preventing it from using Stealth Rock. Stunned by Pikachu's incredible electrical power, Roark reacted too slowly to form an effective counterstrike by using Screech and Pikachu lunged forwards and smashed Onix in the neck with Iron Tail, knocking him out.
- Much like Brock's Onix, Roark's Onix is the Pokémon to be affected by Ash's Pikachu's Thunderbolt, despite the fact that it should be completely immune to it.