You need 100 gems to unlock this level. I have 132.
Toadette finds herself at the ruins of a temple. There are many Mud Troopers in this area. Sneak past them, or use your flashlight to make them temporarily disappear. Walk through the arch, then up the ladder on the other side. It leads to the mine cart. There are Ant Troopers crawling over the temple ruins. Past the temple, you'll find a small pyramid of blocks with a POW Block. Nearby is a lone item block with many coins. You'll also find a brick wall that hides stacks of coins. Break as many bricks as possible, as well as defeat as many Mud Troopers as possible. You'll soon reach the end of the mine cart track. Collect the coins if you like, then dodge the Mud Troopers to reach another one on the opposite side of the coins. Once in the mine cart, pelt the nearby pyramid of brick blocks with turnips, as the first gem is inside. You'll soon go around a corner and find more Mud Troopers and a POW Block. Hit the POW Block to defeat them, then toss a turnip at the second gem. After turning a couple more corners, the mine cart will drop a large distance. There's a wall of item blocks with a POW Block in the center. Hit the POW Block, then immediately take aim at the 1-up Mushroom that appears so you can collect it. Aim and timing are crucial, as it will fall into the void. Immediately look behind you for the third gem. Enjoy the rest of the ride and get the Star.
Special Challenge: Collect the 1-up Mushroom.