Walkthrough: By heading through the door on the right of the main entrance to the castle, you will encounter a number of switches in the middle of the ensuing rooms. When pressed, these switches will show colors in a particular order. After they do, you will need to enter the colors in that exact order or you'll have to begin from the very beginning. However there's a catch: as you try to solve these puzzles, Team Rainbow Rocket Grunts will try to interrupt you in hopes of slowing you down. At the end of these puzzles will be the next room, this one having the Leader of Team Magma, Maxie, inside.
Like Archie, Maxie was brought from a certain universe where he was successful in causing the Hoenn Region to dry up, thus creating a world where people and Pokemon had more land to live on without conflict. Again, it isn't clear if he was never defeated by the heroes of that region or if he had yet to face them, but he'll say he was pulled away right as he was successful in fulfilling his plans. And just like Archie, he is set on duplicating his goal in this universe.
Team Magma Maxie - Level 64 Mightyena, Level 64 Crobat, Level 64 Weezing, Level 64 Camerupt, Level 66 Groudon
After defeating Maxie, you will need to press the button behind the painting on the back wall in order to continue onward. As you reach the main area to the castle after both Team Magma and Team Aqua having been defeated, the gates upstairs will open as Guzma will hold off more Grunts. Guzma will then force said Grunts to describe how you will need to open the warp pad to the Preservation Area, as well as find a special key card to access it. After telling you this, Maxie and Archie will appear and begin fighting with each other, saying they had already defeated the other in their given universes. However, before getting into it, they will mysteriously disappear.