Captain Toad starts off at near some palace gardens. There's a Double Cherry to the left. With it, Captain Toad gains a clone. Move them towards the P-Switches to split them up. This makes a wall to the gardens drop so they can go explore. Use the hedges to split them up. There's a creature wandering around underground with a plant-like structure on its head. Corner it or stun it with a turnip, then pull on the plant to pull it out of the ground. It will give you the first gem. Be sure to pull all of the plants. Keep the clone separated from Captain Toad and carefully navigate the hedge maze so they can hit the P-Switches on either side. This will make walls appear that divide the hedge maze in half and drop down the walls in the back. Move towards the back and drop down. They'll enter a 2D area with P-Switches and Shy Guys. Alternate hitting switches, which will allow them to drop down and stomp the Shy Guys. The coins will trigger the appearance of more coins. On the left side is a doorway that doesn't exist on the right. Go through it to find the second gem. A little lower, you'll find two doorways. Go through both and you'll find another plant creature. Pull the plant for third gem. Walk back through the doorway so that one of the Captain Toads steps on the P-Switch. This will allow them to reach the bottom of the palace. Have them step on the P-Switches at the bottom, which will remove the wall between them so they can join up. Grab the coins on the way out to an elevator that requires two people to activate. This will take you to the Star. You'll get 10 coins for getting the Star with the clone.
Special Challenge: Collect 70 coins.
You must collect every single coin, from the coins you get from the clone, plus coin plants, plus turnips.