Sarasaland Adventure v4.0 (SMBX) - Heavenly Heights Fortress (6-4)
Info: https://rpgmaker.net/games/4216/
We go from Kirby to Yoshi's Island now with this fortress level, which is quite nice; it also looks like something that would probably fit better in World 3, but it doesn't matter I guess. While this level is easily the shortest level in all of World 6, it does require switchblock manipulation to get most of the goodies and to progress through, like level 2-4 did. You also get to use those chickens to jump high in a few places, like in 6-1. There are also a few dangerous sections, like that bridge of alternating ! blocks across the lava in the first room, or when trying to get the second star right before the miniboss room.
Speaking of the miniboss, it's none other than Petey Pirahna. This fight is actually quite difficult because not only can his spraying attack reach you from practically anywhere in the room, but you also must wait until the front part of his "egg cage" opens so you can toss a bomb inside and damage him AND you have to wait until the cage comes within your throwing range. Ice Mario makes this fight easier as you can freeze the bulletbills, then pick it up and toss it upwards into the cage. This concludes the clouds section of World 6.