Bowser (2) Card
Make your way all the way to the right where you will find the first door. Once you are through it, go right toward the second pipe you encounter and head down. Use Boomer to take out all the Shlorps, and a chest will appear with the Bowser (2) card inside.
Moon Cleft Card
From the Bowser (2) card, exit back through the pipe and head left over the mountain. The Moon Cleft Card is located in the first valley. Toggle to 3D mode and there will be a chest containing the card.
1st Block Puzzle
From the Moon Cleft Card, make your way back up out of the valley and use Peach's umbrella to hover over the gap. You will encounter a set of three blocks. Hit them in the following order: Left, Right, Middle. This will cause a pipe to appear leading you to the next puzzle.
2nd Block Puzzle
Coming out of the pipe, head right and switch to 3D to avoid the Muth. If you have Bowser's flame breath ability, use it to kill the Muth and be rewarded with 1,000 points each. You will eventually encounter three more blocks, which require you to hit them in a precise order: Middle, Right, Left, Left, Right, Middle, Right, Left, Right, Right, Middle, Right, Right, Left, Middle, Middle, Left, Left, Left, Right, Left, Left, Left, Middle, Middle. This will reveal another pipe that will lead you to the Star Block. Hit it and make your way to Chapter 5-2.