The Cyllage Gym exists within a large cave containing an underground waterfall. The Gym provides a bench in the rear where the player can sit and view the waterfall. A large, rocky hill takes up the center of the Gym, which is covered in rock walls that the player must climb in order to reach the top. After defeating Grant, the player can slide down two slopes for a shortcut to the entrance of the Gym.
The Cyllage Gym appeared in Climbing the Walls!, where Ash and his friends visited it for Ash's Gym challenge. Like in the games, the battlefield is located on the top of a tall climbing wall, but there is also an elevator for those who wish not to climb.
Before the battle, Ash was informed that he was allowed to use all of his current Pokémon in hand against Grant's two Pokémon, as Grant wanted challengers to come at him with everything they had. Thanks to Ash's intensive training after witnessing Grant's battle against Viola at the Battle Chateau, he was able to counter Grant's Onix's Rock Tomb by having his Froakie jump on the boulders, a tactic he had dubbed as "Rock Tomb Climb". Thanks to this method, Froakie was able to get close enough to finish Onix with a super effective Water Pulse.
Grant's second Pokémon, Tyrunt, proved to be a much tougher opponent, surprising Ash with its amazing jumping skills and ability to use Draco Meteor. With these factors on its side, Tyrunt managed to defeat both Froakie and Fletchling, although not before receiving some damage from them, leaving Ash with just Pikachu. Even though Tyrunt as a Dragon-type had the type advantage over Pikachu, Ash was able to come up with a counter method for Draco Meteor, having Pikachu jump on it by using Iron Tail, thus evolving "Rock Tomb Climb" into "Draco Meteor Climb". Afterwards, Pikachu sent one of Tyrunt's Rock Tomb rocks into the Royal Heir Pokémon's mouth with Iron Tail, and then finished it with a Thunderbolt, earning Ash the Cliff Badge.
Pokémon used in the Gym
Onix is Grant's first known Pokémon which he used in a battle against Viola's Surskit at the Battle Chateau. Despite Surskit creating its signature ice battlefield to aid its speed, Onix was able to turn the tables on the Pond Skater Pokémon by using its masterful control of Rock Tomb to trap it and Rock Polish to increase its speed, keeping Surskit on the defensive. Eventually, Onix ended the battle by using its powerful Flash Cannon to knock Surskit out. It was seen in flashbacks in A Pokévision of Things to Come! and Coming Back into the Cold!.
Onix reappeared in Climbing the Walls! as the first Pokémon Grant used in his Gym Battle against Ash, going up against Froakie. Onix attempted to keep up with the Bubble Frog Pokémon, but Froakie's speed in combination with Double Team confused Onix, leaving it open to attacks, which eventually allowed Froakie to knock it out with Water Pulse.
Tyrunt was the second Pokémon used by Grant in his Gym Battle against Ash. Tyrunt, unlike Froakie, was quick, and while Froakie was able to dodge Rock Tomb, it was easily overpowered by Tyrunt's Draco Meteor. Tyrunt next went up against Fletchling and managed to knock it out easily (but not before taking damage from a super-effective Steel Wing).
Finally, Tyrunt went up against Pikachu, who was able to dodge Tyrunt's attacks and even used the projectiles from Draco Meteor for momentum before managing to wedge a rock in Tyrunt's mouth and finally knocking it out with a direct hit from Thunderbolt.