Character: Iwark (Hyouta)

Onix is a subterranean creature that bores its way through the ground at a rate of 50 mph (80 km/h) in search of food. The tunnels it leaves behind as it burrows through the earth are used as pre-dug homes by other subterranean Pokémon such as Diglett and Geodude. Within Onyx's member is a structure nigh identical to a magnet, which allows it to determine its heading, its depth underground, and other such information useful for a subterranean Pokémon to know. It acts quite like a compass. As Onix ages, it burrows deeper underground, and its rocky member becomes progressively harder, rounder, and smoother. Around the age of 100, the pressures exerted on its stone member become so high that it is compressed into a much harder, diamond-like composition, although it is closer to metal in nature.

In the anime, an Onix is owned by Brock as part of the many Pokemon owned by the training gym that Brock's family runs. Brock had initially received the Onix from his father, who is a specialist in rock-type Pokemon. When Brock feels the need to travel with Ash Ketchum yet again, he entrusts the care of the Onix to one of his many younger brothers. This takes place in Pokémon Chronicles. It eventually evolves into a Steelix.

Ash and Misty first heard about the Crystal Onix when they picked up a bottle in the ocean with a note in it written by Marissa asking anyone if they knew anything about the Crystal Onix to tell her. Tracey explains to Ash and Misty that it's supposed to be an Onix made of glass crystal but he said he wasn't sure it was real. Tracey states that there were people who said they've seen it but they were only rumors. Ash stated at the time he'd love to see the Crystal Onix and his wish came true when he saw it.

Team Rocket heard the rumor about the Crystal Onix from some local merchants and decided they would try to capture the rare Pokémon. The Crystal Onix just hit it with its tail and sent Team Rocket blasting off again.

The Crystal Onix lives on a remote part of Sunburst Island in a cave. When the tide goes down, a sandbar appears to let people get to that part of the island. It isn't afraid of water like most normal Onix are and it often spends time in the underground lake in the cave. Mateo battled it and knocked it out but before he tried to capture it, he felt something strange for a minute when he looked at the Onix. Mateo explained that the feeling was hard to describe but he gained the inspiration he need to start working again on his Pokémon statues thanks to the Crystal Onix. The Crystal Onix then recovered and dove back into the water after Mateo thanked it.

Janina's Onix was treated with a water-resistant polish for her battle against Ash.

Onix is one of the Pokémon that resides of an island among the followers of the Meowth of Bounty.
When Team Rocket's Meowth land on the island and could not use Pay Day, Shimajio suggested that this could be a test of their beleifs and decided to give Meowth some battle experience on the island's battle arena in an attempt to make to learn Pay Day.
Onix battled Meowth after hitting it with its tail and then using wrap on it. The battle was interupted when Jessie and James had aided him by throwing their remaining money and bottlecaps to make it look like Meowth had used Pay Day.

Bruno's Onix was a wild Onix that traveled on Mt. Hideaway and tried to trample anyone in its path. After Bruno saved Ash after he had fallen into a pit inhabited by it, Bruno eventually figured out what was troubling the Onix. A Sandslash had lodged itself in between one of the Onix' many rocks. After Bruno removed the Sandslash from the Onix, he asked the Onix if it wanted to come along with him, to which the Onix happily agreed.

Brock received it as an Onix as a birthday present from his father, Flint.

Orange League Final - Vs. Ash Ketchum (Rocky Field)

Pikachu had given Ash the advantage by defeating Drake's Ditto but was very Tired.

Drake selected Onix and Ash recalls an exhausted Pikachu to be replaced by Squirtle. Ash makes the first move and has Squirtle use Water Gun, but, before it can connect Drake has his onix use Dig and it goes underground. Squirtle headed towards the water pool in the middle of the arena but Onix emerged just before it reached it and then managed to trap Squirtle in Wrap.

Squirtle struggled to get free but the Wrap was too strong, however, Ash managed to get Squirtle to use Hydro Pump which managed to strike Onix and release Squirtle from the Wrap attack. Squirtle used Skull Bash on the Onix and eliminated Drake's second Pokémon in the battle.

Grant's Onix was first seen battling Viola's Surskit at the Battle Chateau. Viola noted that its speed and power has increased since last time they battled. That increase proved to be the difference in the battle as it overwhelmed Viola's Surskit and defeated it. Grant was awarded the title of Grand Duke to which he thanked his Onix for all its hard work and dedicated the victory to it.