Block World is a reoccurring area from the original game, it is accessible from the Sewers. Mafurako can be found here. The background image is the same as the one from the original game.
Interacting with Mafurako will cause her to vanish and reappear somewhere else. Doing this 6 times will unlock the door to Snow Valley. A black sculpture can be found to the left on top of a tall block that will show a hint to help you find Mafurako.
Interacting with the Bathroom changes your camera angle, which can be helpful for platforming.