In this castle, there are many spikes bars formed into squares. They'll flip around in a set path. Be careful when jumping over or through them. Grab a Super Bell and deal with the Chargin' Chucks ahead. There are some platforms that swing back and forth. Trigger the Green Ring and collect the Green Coins on these platforms for the first Green Star. Up ahead is a warp box that takes you tot he midpoint.
Here the square spike bars roll on their sides from the walls. Avoid a few of them by climbing the wall, which is where the stamp is. Drop back down because one of the later square spike bars has the second Green Star. If it rolls off the edge, wait a little while and it will come back. There's a Chargin' Chuck in the area. Ahead, the square spike bars will fall towards you, on top of the springboards. Jump carefully. At the end is a warp box. Before you go through it, climb up the wall to find an alcove with the third Green Star.
The warp box takes you to King Ka-Thunk, a square enemy that moves around using a square spike bar. He'll try to hit you by falling over or running into you with the spikes. When he falls face first, stomp the X on his back. After a hit, he'll make two corners of the arena disappear. After the second hit, he'll make the other two disappear. Three hits will defeat him. The warp box to the flag appears. Free the purple Sprixie Princess. She'll use a wrench to build a clear pipe to World 6.
The stamp is of a Chargin' Chuck.