From Bulbapedia, the community-driven Pokémon encyclopedia.
Crystal Colosseum (Japanese: クリスタルコロシアム Crystal Colosseum) is the fifth Colosseum in Pokémon Battle Revolution. The battle theme is Tournament Battles, much like the Battle Dome in Pokémon Emerald. The Colosseum leader is Colosseum Leader Voldon. Unlike most other Colosseums, there are only 5 battles in all.
Crystal Colosseum is located in an underground cavern on the other side of the island from Pokétopia. It is lit by glowing crystals situated on the walls and floors, thus giving it its name. Stalactites, stalagmites, and pools of water are everywhere.
The battle theme, Tournament Battle, pits Trainers against each other in an elimination tournament, with the winner of each battle advancing to the next round. The tournament starts off with 16 Trainers. This is narrowed down to 8 after the first round, and then to 4 during the second round, and then to two Trainers after the third round. The winner of this battle earns the right to challenge the Colosseum Leader, Voldon (In this manner, Crystal Colosseum is different than the Battle Dome, as Voldon does not participate in the elimination tournament, and can therefore not be eliminated, as opposed to Tucker, who does partake in his own tournament).
After you beat the game, you may select the level 50 All rule. The rules do not change, but the order of the brackets does.
Beating Crystal Colosseum for the first time in Level 30 Open mode gets you a Pikachu Bag, a custom battle pass with Crystal Colosseum in the background, 9 items in the shop, and 550 Poké Coupons. Beating Crystal Colosseum for the first time in Level 50 All mode unlocks 23 pieces of gear in the shop. Also, when the player beats Voldon for the first time in Level 50 All mode, they obtain his Electivire outfit. There is a small chance of Voldon wearing a shiny outfit when you battle him in Level 50 All mode. If the player beats him while he is wearing a shiny Electivire outfit, they will obtain a shiny Electivire outfit of their own.
The default mode of battle here is Double Battle. An option to change this to Single Battle is unlocked after beating Rank 1 for the first time.
The Pokémon and Trainers are not set, except during the first time you battle there, at Rank 1 Level 30 Open, and the first time you battle using the Level 50 All mode, Rank 1 Level 50 All. The Trainers, and the Pokémon they have, go as the following during Level 30 Open, Rank 1: