World Bowser-5: Deepwater Dungeon

You'll start in a room where the water level changes. Head underneath the wall on the right side and swim upwards. If you're feeling impatient, you can wall jump your way up. You'll eventually reach some spiked blocks.

Look for a higher body of water and jump into it. Make your way to the top left corner of this area to find the Stamp.

In the same section, check the lower right corner for some ?-Blocks. One of them contains a Super Bell power-up, which you'll definitely want to grab.

Continue swimming upwards, above where you found the power-up, until you reach dry land.

You'll need the Cat Suit for the next part, so make sure you have one! Look for an opening up and to the left of where you just exited the water. Climb up into this hidden alcove to find Green Star #1.

Proceed to the right until you reach the Checkpoint Flag. After touching it, board Plessie. There isn't much to find in this Plessie section besides some coins and Madpoles, so just focus on moving forward.

At the end of the Plessie ride, climb the wall to the left or right of the opening to reach a ledge. Climb further up to find Green Star #2.

Jump down and cross the donut blocks. Swim up to the next ledge, where you'll find another ?-Block with a power-up.

The next area involves swimming through small pockets of water, transitioning between them while dodging moving spiked blocks.

When you reach the end of this section, don't go into the pipe immediately. Instead, climb the wall above it. This will lead you to a cloud cannon.

Race through this bonus area to collect Green Star #3. You'll then be transported near the Goal Pole.

Use the moving water to help you reach the top of the Goal Pole for an easier finish.