The final castle alternates platform puzzles with seven Koopaling trials. Refill HP and BP before entering each red door, then save between encounters. The galleries below follow the original Game Boy Advance route.
Iggy’s Room
Cross the opening platforms without dropping into the Boo area, using Spin Jump for the longer gap. Iggy makes the brothers dizzy before his trial, reversing their movement. Take a moment to test the directions, then steer around the fireballs and reach him before the effect wears off. During the battle, watch which brother each fireball targets and use the matching button to jump. Save BP for attacks you can execute reliably.
Morton’s Room
Approach Morton by jumping his ground shockwaves with ordinary jumps. High Jump and Spin Jump do not clear this trial correctly. In combat, his stomps send more waves across the floor, so wait for each wave to approach instead of mashing both buttons. Keep Mario and Luigi healthy before finishing the battle; the raised platform opens the route to Lemmy.
Lemmy’s Room
Watch Lemmy before he mixes himself among his copies, then strike the real Koopaling with the hammer. During the fight, keep track of the genuine Lemmy when the duplicates appear and focus your attacks on him. Jump his fireballs with the targeted brother. Winning activates a fountain: return to the fire-blocked route and use the water to put out the flames.
Ludwig’s Room
Ludwig tests your timing by rushing across the room inside his shell. Jump when the shell reaches the brothers, and watch for pauses that try to draw an early jump. Once the trial is over, the battle combines fireballs and shell attacks. Do not leave until you have used the switch made accessible by his defeat; it raises the next platform toward Roy.
Roy’s Room
Separate the brothers vertically: put Mario on the higher ledge while Luigi follows the lower route. Activate the Simu-Blocks together to build the path over the lava. Roy retreats when you reach him, then ambushes you as you leave. His Time Bob-omb imposes an eight-turn limit, so spend BP on your strongest dependable Bros. Attacks. Watch his shell rushes and jump the shockwaves rather than sacrificing turns to repeated healing.
Wendy’s Room
Work through the hammer trial and strike Wendy twice in succession to start the encounter. In battle, track the real Wendy among her copies. Her expanding rings close around the brothers; time the jumps for the rings instead of treating them like straight fireballs. Another Time Bob-omb limits the fight, making focused damage more useful than attacking every duplicate. The platform raised by her defeat leads to Larry.
Larry’s Room
Keep Luigi inside the barrel for the fireball-rally trial. Stand in the line between Larry and the Bob-omb and return the fireball; Larry volleys it back with his racket. Continue until the rally hits him. During the battle, answer his returned fireballs and spinning attacks with carefully timed counters. Watch the Time Bob-omb and use Bros. Attacks early. Defeating Larry removes the spikes on the route to Fawful.
Fawful and the Throne Room
After Larry, continue through the newly opened passage and save before Fawful. Wait for an opening when his protective equipment leaves him vulnerable, then use Bros. Attacks to deal damage. Restore the brothers before entering the throne room: Bowletta is followed by a second final encounter, so keep healing items in reserve.