Bowser's been freed from the safe, so the bros return to him. Starlow wants advice, but Bowser's back hurts and he can't move. The Lumbar Nook is reacting, but first go to Toad Square. Talk to Toadbert on the top level. He's been having a weird dream. In it, he's drinking tea and time is passing slowly. Then, he hears (A)(B)(X)(Y)[L][R](Y)(X)(B)(A) being pressed. Time starts passing quickly. Now, with that little information, head to the Lumbar Nook.
Toadsworth is there, enjoying some peace and quiet. The bros explain that they came to heal Bowser's back. Toadsworth noticed the floor became hard and darkened. He suggests stimulating the spot in the center, but his cane isn't enough. Have the bros drill into that spot. It starts working slowly. Toadbert appears and wants to watch. Their dialogue emphasizes that this process will take a while. They have tea and Toadsworth sets an alarm for when the process will be done. You can let the process go on its own, which will take several (more than 5, possibly more than 10 minutes), or start pressing the buttons from Toadbert's dream. The alarm should go off within seconds of entering the 10-button combination. The area returns to its normal color and Bowser feels his back loosening up. He feels better than normal and is flexible enough to roll into a ball. He can safely roll over spiky areas. This is the spike ball move, which allows him to roll up areas with soft dirt and destroy statues. Use [R], then hit (X) to roll into a ball, then roll around.
Starlow informs Bowser that he's in Peach's Castle, the Dark Star will awaken soon, and that he needs to save Peach. Roll up and out of there. Go south twice and destroy the Fawfulized statues. One of them has a Chakroad. Bowser has to deal with the enemies here. One Mechawful has a Blitty. Roll up into the turret to get into the castle. Inside, you'll find Alarm Bob-ombs and Naplocks. Inhale the Alarm Bob-ombs. A Naplock has a Blitty. Go west twice and you'll come across three Fawfulcopters with keys. Fawful says, "Fawful won't lie. Fawful has shock at you getting here. But that shock turns to chortles as you stop here! There are doors here that need keys, and Fawful has them! You will wander forever in my modified castle of Peach until you cry from lack of doors!" Bowser says he'll break the doors down. "You have energy like a little angry battery with no friends. But even if you get past the doors, the castle of Peach... Oh, but I have secrecy! Fawful says no more! Are you catching my Fawfulcopters?"
Go south to the dining area. There's a Save Block and the Fawfulcopter with the blue key. It's behind the statues which you can destroy by rolling. It will fly off and go west. Follow it south, then back north again. It goes into the hole in the wall. You'll find Dark Trashures here, which give more money than regular Trashures. One of them has a Blitty. Roll up the back wall onto the stovetop to enter a different hole in the wall. Chase the Fawfulcopter out of there and follow it south. There are Dark Mechawfuls on wheels to deal with. One of them has the last Blitty you need. When the Dark Mechawful starts counting down, just before it reaches zero, punch to counter it. Duck when it fires a beam, then punch it when it stops. If Dark Fawful Guys appear on the top screen with a bomb over the enemies, inhale them to make the bomb drop. This will give you a great advantage in battle, if not end the battle entirely. The Fawfulcopter goes to the south over a spike pit. Push the green, shell-like device to the back to launch Bowser into the Fawfulcopter, making it drop the key.
Once you have all fifteen Blitties, give them to Broque Monsieur. The Blitties lie around the shop. Broque Monsieur gives Bowser a Block Band, Block Fangs, and a Block Ring. He also lets Bowser take him for a walk, which gives Bowser the Special Attack Broggy Bonker. Use the stylus to clean the dirt off of Broggy, then he'll attack the enemy twice, with all fifteen Blitties in tow. It is an incredibly powerful and cute attack.
Go through the northeast doorway, then go north through the door on the left to another spike pit with the green key. Follow it around and pin it into the wall to get the key. Go north, then west to the Save Block, then west to Peach's room, then west twice to a dirt wall. The Fawfulcopter with the red key is here. Follow it up the dirt wall and get the red key. Go north of the Save Block to find the doors the keys unlock. The green door has an Economy Ring, which reduces SP costs by 50%. The red door has a bunch of Magikoopas in a cage. Free them and Bowser can use Magikoopa Mob. Use the stylus to draw lines to light up every Magikoopa's wand to attack the enemy. The blue door leads to a spike pit with another shell-like device to launch Bowser. There are items to get here, so push it back varying lengths. To move forward, push almost all the way back and go through the left doorway on the top. Heal and save.
To the north, you'll see a machine with time bombs. Go east three times to a dirt wall. On the right side, on one of the platforms, you'll find a couple of gears. Spin them to raise a gate to the left. Quickly climb to the left to pass through before the gate closes. This requires precise controls, so it may take a few attempts. You can also go to the platform above and drop down. Roll west, then drop down the dirt wall and go west. This leads back to the room with the time bombs. Roll on the treadmill to lower the wall and use the time bomb to blow up the cracked wall. Go west three times from the room with the time bombs. Electricity will crackle on the floor below. Jump over the Bob-ombs and go east twice. Roll on the treadmill and blow up the wall. Go north twice, heal, and save.