You'll need 100 Green Stars to unlock this level. This level takes place inside and outside a Japanese-style house with music to match. You'll start in an empty hallway. Touch what looks like the back wall using the Game Pad to make the doors slide open, revealing a pipe. Go through the pipe to a room with Goombas. Get a Boomerang Flower from the item block. You can now throw boomerangs, which give you a range attack with the potential for combos. Touch the door to the right and go behind the wall. Go all the way to the right and you'll find an invisible block with an item in it. Go back left and open the door. Carefully go up the ramp, as there is a Spike throwing spike bars down the ramp. Go left and open the doors to reveal two P-Switches. Take out the Galoomba before it hits you. The left P-Switch lowers the stairs to the left. The right P-Switch makes two Goombas appear. Kill them for Goomba Caps. When wearing the Goomba Cap, enemies will not notice you. If you run into an enemy, you'll lose the Goomba Cap.
Go up the stairs and ring the gong (by touching it on the Game Pad) for lots of coins. Ahead are more sliding doors. The first Green Star is behind these doors, but you have to wait for the wall to move first. Just ahead is a clock and an invisible Moneybag. To the right is the warp box behind some doors with many Goombas to the midpoint, which is outside. This is part of the building's roof. There are Thwomps, Spikes, Goombas, and Key Coins here. The second Green Star is nearby, in the gap to the right. Jump the gap or use a boomerang to get it. On the other side of the gap are Propeller Blocks. When wearing them, press (A) to jump, then hold (A) to fly. You can only wear one item at a time, so if you want the Propeller Block, lose the Goomba Cap by taking damage. The five Key Coins are all over here, but not hard to find. Check the top levels of the roof if you're missing any. The warp box is on the top level.
The warp box takes you back inside. Ringing the first gong makes Goombas appear, but the second one makes coins appear. Ahead, you'll run into a few sets of Spikes. Kill the first three you find. Walk towards the front wall, where the spike bars were going and you'll wind up outside. If you still have the Propeller Block, fly up onto the roof and you'll find the stamp on a cloud. It's well hidden. Carefully drop down and go back inside. There are more Spikes inside. To the right, you'll find a warp box and a gong. Ring the gong to make a Mystery Box appear. This takes you almost outside, where a Spike is waiting in a cage on the side of the building above where the Thwomps were. Kill the Spike for the third Green Star. Go through the warp box, which takes you to the roof and the flagpole. There are golden Cheep-Cheep statues. Hit the triple item blocks under the Spike to defeat it, allowing you to reach the flag more easily.
The stamp is of a Moneybag.