First of all, enter a name. This is used for your name and the name of the savefile.
Then you will show up at the reception desk. The receptionist named Anna will greet you and talk to you about Pokétopia for a bit, then let you choose between two Rental Passes. Pick one, and then you can explore the game.
Custom Passes And Your Own Pokémon
After Anna finishes talking to you, go to the part of the menu called "Check Storage". Anna will talk to you a bit more about how to Sync up your Pokémon. Go to the next part of the menu called "Get Pokémon". The Game will explain how to get your Pokémon from any Generation IV Pokémon Game. After you Sync your Pokémon, go to "Check Storage". Your Pokémon should be there!
Creating A Custom Pass
After syncing your Pokémon, go to the part of the menu called "Custom Passes". Anna will talk to you some more about Custom Passes. After she is done, click create pass. Right now, there are only 3 pass designs to use, but the more Colosseums you beat, the more designs you get. Chose the design you want, then the game will prompt you to pick your Trainer model. Now type in your name, and your first pass is ready for some Pokémon!
Now that you've created the pass, click on the little circles on the pass. Once you click on one, the screen with all the boxes will pop up. Click on the box that has the Pokémon you want in it, then click the Pokémon and it will appear on your pass. Finish your pass by putting all the Pokémon you want on it. keep in mind that you need at least 3 to participate in all of the Colosseums.
If you want to customize your pass more, click on your Trainer. This will lead you to a screen with options for the gear your Trainer is wearing, the pass design, your Trainer quotes, your Trainer class, and the picture style on the pass.
Now all you need to do is challenge the Colosseums!
Gateway Colosseum floats at the entrance to Pokétopia and is lit by bright neon lights. All battles here are depicted as happening at night.
The battle theme, Rental Battle, requires one to use only Rental passes in this Colosseum. Custom passes are barred; you may not use your own Pokémon here. However, once you beat all 7 battles, you get to keep the Rental Pass you used. At the start of the game, there are two Rental Passes to choose from, the Red Rental Pass and the Blue Rental Pass; you can either use the one that you didn't get at the beginning and unlock it, or use the one you got and return after claiming victory to challenge Rank 2 and earn the other Pass. After you beat Waterfall Colosseum their will be two more passes to unlock, the Purple Rental Pass and the Green Rental Pass. After beating Sunny Park Colosseum, the last two passes, the Grey Rental Pass and the Yellow Rental Pass, will be available.
Beating Gateway Colosseum for the first time in Level 30 Open mode gets you a Bronze Badge, a custom Battle Pass with Gateway Colosseum in the background, and 280 Poké Coupons.
Also, the default mode of battle here is Single Battle. An option to change this to Double Battle is made available 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. The Trainers, and the Pokémon they have, are as follow during Level 30 Open, Rank 1.