When you've chased and tagged the fake Mario in all seven areas, you'll find Delfino Plaza flooded and the bad guy waiting at the cave behind Shine Gate. This passage leads to Corona Mountain. There's only one objective here--defeat the enemy and save Peach.

The first section is full of hazardous jumps. Observe the timing of the spiked panels, and always hover over the flaming panels to extinguish them before you land. There's an extra life on your way, and when you reach the area where the small boat is docked, you can refill your water reservoir with the fountain on the left and grab one more one-up in the crate to your right. After that, it's time to hop in the boat for an even more dangerous part of the level.

Stand near the back of the boat to propel yourself, and move to the front and spray to the side if you need to turn sharply. Above all, be careful and take things slowly. If you so much as scrape against a rock, the boat will sink and you'll be toast. There are blue coins surrounding the platform where the rocket nozzle waits, so try for a few if you're feeling brave. When you're ready, hover to solid ground and grab the rocket.

Blast straight upward to find yourself standing on a cloud. Adjust the camera until you can see other clouds above you. Boost yourself up again. You'll be able to see a one-up in the middle and moving clouds above you. Land yourself on the next set of moving clouds, then boost up until you hit a red cloud and find yourself facing down the final boss.

Work your way up the clouds to reach the final encounter.

You're on the rim of a gigantic hot tub filled with an extremely hot green substance. Bowser sits in the middle and spits flame, occasionally shaking up the tub and sending waves of boiling fluid at Mario. Junior is in a boat that will launch bullet bills at you. Neither can be damaged, but the strategy to beat them is fairly simple.

First, be aware of the projectiles Junior fires at you. You can easily blast them out of the air with your water cannon. Pay special attention to the light-blue ammunition. It will hone in on you, but it also can contain valuable items like extra lives and water bottles. Your plan of attack is to break the four corner pieces marked with a fireball by rocketing into the air and coming down hard with a hip-drop.

Mario busts the place up.

The town will be restored to normal from this point on, and you're free to go back and visit any area of the game. A boat on the southwestern pier will take you back to the airport, where you'll find various coins and be able to get one last shine. See the Your Guide to Delfino Plaza section for details.

Blue Coins
The requirements list the earliest (or sometimes only) episode in which the coins appear, as well as any additional details.

Location: On a platform during the opening stretch of Corona Mountain.
Required: N/A
Method: It's on your way--simply hop and land on it.

Location: In the lava lake.
Required: N/A
Method: You'll need to navigate your rickety boat through a maze of death to collect the nine blue coins surrounding the rocket nozzle. Good luck.