Onix was first used to battle Paul's Elekid and Chimchar in Shapes of Things to Come. Onix had the advantage due to his large size and immunity to Elekid's electric attacks. Elekid managed to paralyze Onix with Static, but Onix used Stealth Rock, so Paul recalled Elekid and replaced it with Chimchar. Chimchar avoided Onix's attacks by using Dig and defeated Onix.
Onix appeared again when Roark battled Ash, easily defeating Turtwig with a single Double-Edge. Onix then battled Pikachu and won by unleashing a Screech, blowing Pikachu into a rock, defeating him and winning the battle.
Onix battled Pikachu a second time during Ash and Roark's rematch. During the battle Pikachu used a Thunderbolt that was powerful enough to actually hurt Onix. Stunned by Pikachu's incredible electrical power, Roark's reacted too slowly to form an effective counterstrike and Pikachu lunged forwards and smashed Onix in the neck with Iron Tail, knocking him out.
|Slam||Shapes of Things to Come!|
|Double-Edge||Shapes of Things to Come!|
|Stealth Rock||Shapes of Things to Come!|
|Screech||A Gruff Act To Follow!|
|+ indicates this Pokémon used this move recently.*|
- indicates this Pokémon normally can't use this move.
- Onix is the second Onix to be affected by Ash's Pikachu's Thunderbolt, despite the fact that it should be completely immune to it.
- The first was Brock's Onix.
- In the games, Screech is used to lower the opponents defensive power but does not actually do any damage.
- However, Onix's Screech is so powerful that it can actually hurt its opponents.