The Lumiose Gym is a high-tech tower known as the Prism Tower. It is initially inaccessible when the player first reaches Lumiose City as it and much of the rest of the city have lost power due to a blackout. After the player has defeated Team Flare in the Kalos Power Plant, power will be fully restored to the city and the player will be able to challenge Prism Tower.
The Gym features groups of elevators guarded by the Gym's Trainers on several floors. On each floor before the sixth (where Clemont is), Bonnie will quiz the player about a Pokémon's silhouette as a multiple choice question, and the player must choose the elevator corresponding to the correct answer. The player must battle the Trainer guarding the elevator they have chosen before they can enter the elevator and know whether they have chosen correctly. If the player has chosen correctly, the elevator will ascend to the next floor, but if they have chosen wrongly, they will have to try another elevator.
The quiz choices and correct answers are as follows:
Any Trainers the player did not battle before moving to the next floor cannot be battled if the player returns to that floor. Any elevator the player used to ascend to a floor can be used to either return to the previous floor or directly to the first floor.
Prism Tower appears as a playable stage in Super Smash Bros. for Nintendo 3DS, serving as a hallmark for Lumiose City. Matches begin on the ground level of the tower in front of the building, and players must climb the tower by securing footholds (such as moving platforms). As the stage ascends, the background scenery changes to a different time of day.
In Clemont and Bonnie's backstory in the anime, Clemont had created a robot called Clembot to cover for him when he found he had little free time due to his duties as a Gym Leader. However, his intended passcode wasn't recognized, so Clembot kicked him and Bonnie out of the Gym. After many failed attempts to reenter the Gym, they gave up. Over the next few weeks, it gained a bad reputation for shocking and violently ejecting challengers for either having less than four Badges or losing the Gym Battle.
Unaware of the Gym's reputation, since he was a newcomer to Kalos, Ash went to the Lumiose Gym first in Kalos, Where Dreams and Adventures Begin! after learning that the Santalune Gym was closed at the time. As Ash was about to challenge it, he was denied access as he had no other Badges from the Kalos region, resulting in him and Pikachu falling victim to Clembot's ejection policy. Fortunately, the two were saved by Clemont and Bonnie, who had seen them enter the Gym.
The Gym's exterior was featured heavily in Lumiose City Pursuit!, as Professor Sycamore's rampaging Garchomp climbed it. Ash went up after her to calm her down, but she still caused a fair bit of damage to the tower, to the point where parts were too weak to support even Pikachu's weight.
It later appeared in full in Clemont's Got a Secret!. Ash and Serena discovered that Clemont was the Gym Leader until Clembot took over. After discovering the negative impact Clembot was having on challenger attitudes towards the Gym, Ash and his friends go to the Gym to take it back from Clembot. In the end, the Gym was passed on to the newly-reprogrammed Clembot while Clemont is traveling.
It reappeared in A Fork in the Road! A Parting of the Ways!, when Clemont began his training for his battle with Ash, bringing his Pokémon from the Gym to his active party. The Gym was the site of the Gym battle in The Moment of Lumiose Truth!. After the Gym battle, Clemont once again left Clembot in charge while continuing to travel with his friends.
In A Towering Takeover!, after Ash and his Pokémon had been captured by Team Flare, Lysandre had both them and Alain brought to the top of the Prism Tower, where he told Alain about his true intentions of changing the world. Upon learning the truth that he had unknowingly been helping Team Flare in fulfilling their plans, Alain was shocked and devastated. Lysandre then attempted to take control of Ash and his Greninja in order to use their Bond Phenomenon for his own purposes, but Ash defied him, breaking free of the binds he had been confined with. Alain proceeded to help freeing Ash's Pokémon, having finally understood that Lysandre needed to be stopped. The two Trainers then began battling against the Team Flare Boss, with all of Ash's Pokémon and Alain's Mega Charizard X facing against Lysandre's Pyroar and ShinyMegaGyarados.
Meanwhile, at the bottom of the tower, Clemont, Bonnie, Serena, Clembot, and Blaziken Mask encountered Mable and Bryony, who were guarding the entrance to the Gym. Serena subsequently left with Professor Sycamore and Mairin in order to rescue Mairin's Chespie from Lysandre Labs, while Bonnie and Blaziken Mask went after Squishy, whom Team Flare later managed to place under their control as well, leaving Clemont and Clembot together to battle the Team Flare Scientists. After eventually defeating and subduing the two Scientists, the duo entered the Gym in order to retake it. In The Right Hero for the Right Job!, they managed to enter the Gym, where Clemont encountered Xerosic. The two men of science started to battle while Clembot hacked into the machine controlling the two Zygarde. Clemont finally managed to defeat Xerosic's Pokémon, after which Xerosic was ejected out of the Gym by one of Clembot's trap doors. Unfortunately, when Clemont then prepared to shut down the control machine, Clembot revealed that the forced shutdown would also cause critical damage to its main memory, destroying it in the process. Clembot assured Clemont that this sacrifice needed to be done in order to stop the ongoing crisis and save the world. Reluctantly, Clemont agreed to this, sacrificing Clembot in order to destroy Team Flare's control machine.
As Clemont was retaking the Gym from the inside, Ash and Alain's battle with Lysandre was briefly interrupted by Malva, who revealed that she was opposing Lysandre's plan of destroying the world. In Rocking Kalos Defenses!, Ash and Alain finally managed to defeat Lysandre, but despite this and losing the control of both Zygarde, his confidence didn't falter. He then, much to everyone's shock, threw himself off of the tower, seemingly committing suicide. Ash, Alain, Clemont, and Malva subsequently left the Prism Tower in order to help stop Lysandre's secret weapon: the Giant Rock.
In Battling with a Clean Slate!, after the Team Flare crisis had ended and the Lumiose Gym and Clembot were being repaired, a Trainer named Alvin showed up at the Gym. He had lost a Gym battle against Clembot in the past, and now wanted to have a rematch with the robot. The next day, when both the battlefield and Clembot were ready to be used again, Alvin was given the rematch he had been hoping for. As Clembot had forgotten everything it had previously known, Clemont had to give it some basic strategic advises during the battle. The Gym battle eventually ended in Alvin's victory, earning him a long-awaited Voltage Badge. Later that night, the people of Lumiose City gathered around the Prism Tower to celebrate the tower's official reopening and relighting.
Heliolisk was left in Clembot's possession when Clemont was exiled from the Gym. Later, Clemont allowed Clembot to use Heliolisk in Gym Battles. In The Moment of Lumiose Truth! Clemont used it for his Gym battle against Ash. It dealt major damage to Goodra but lost against Hawlucha.
Magnemite was left in Clembot's possession when Clemont was exiled from the Gym and was ordered to patrol to the Gym and keep out intruders. After Clemont greeted it upon his return, it was initially happy but then remembered its orders and attacked him with Thunder Shock. It continued attacking until Froakie's Frubbles put a stop to it. Later, Clemont allowed Clembot to use Magnemite in Gym battles.
In Battling with a Clean Slate!, Magnemite was the first Pokémon used by Clembot in a Gym battle against a Trainer named Alvin. Despite having a type advantage over Alvin's Vivillon, the Magnet Pokémon was defeated before it could land a single hit on its opponent.
Magneton was left in Clembot's possession when Clemont was exiled from the Gym and was ordered to patrol to the Gym and keep out intruders. Later, Clemont allowed Clembot to use Magneton in Gym battles.
The Prism Tower debuted in Pangoro Poses a Problem, where Alexa visited it in order to have an interview with Professor Sycamore there about the incident with Xerneas and Yveltal in Vaniville Town in preparation for an article of the subject. Once she arrived at the tower, she was surprised to find out that her boss, the Lumiose Press editor-in-chief, was there as well, aware of the fact that both Sycamore and Alexa knew the truth about the incident, which the media had covered with a fake tale of an unexplained explosion. After the editor-in-chief had driven Professor Sycamore away with the excuse of him being a busy man and having interviewed him himself, he revealed his association with Team Flare by promptly burning Alexa's article materials to ashes. He then sent out his Pangoro to kill Alexa, but luckily X and his friends arrived just in time to save the reporter lady. As the editor-in-chief had taken Alexa's Helioptile as a hostage, X stayed behind to battle him while Y, Shauna, Tierno, and Trevor helped Alexa to escape.
X soon found out that, even though he had his Kanga and Li'l Kanga attack Pangoro together in their Mega Evolved state, the Daunting Pokémon had no effort in dodging all of their attacks. With Salamè and Marisso being distracted by the editor-in-chief's two Spewpa's Rage Powder, X's hopes of winning looked non-existent. However, once the two Spewpa had been beaten, X was able to use Salamè's tail flame to burn the leaf in Pangoro's mouth, which had allowed it to sense and dodge incoming attacks. With this advantage gone, Kanga and Li'l Kanga were able to defeat Pangoro. As one of the attacks had made a hole in the wall, Alexa's Helioptile was able to recharge itself with sunlight, promptly shocking the editor-in-chief into unconsciousness and freeing itself in the process.
After the incident, Bonnie, whom Clemont had left in charge of the Gym while being away, noticed the chaos the battle had caused, and realized that one of the 25 Pokémon that had been producing electricity for the tower was missing.
This Gym is tied with the Mossdeep Gym in Emerald Version for the highest amount of common Trainers in a Gym, with both having 12. However, in this Gym, the player only needs to defeat four of them in order to get to the Gym Leader.
Both are the fifth Gyms of their respective region, and both Gyms are inaccessible the first time the player enters their city (though this is not true for the Hearthome Gym in Pokémon Platinum).
Both Gyms feature four sets of multiple-choice questions, and require the player to fight a Trainer if they answer the question incorrectly. However, the Lumiose Gym also requires the player to fight a Trainer even if the question is answered correctly.
Most of the underlings in both Gyms consist of young children and Ace Trainers.