Level By--- Everyone, though in room order
rextep, CosmicTiff, Valentine, Aeon, rextep, SMWizard, Nitrogen, NewPointless, Jolpe, CosmicTiff, Nanigashi-Kun, Centipede, PokerFace, Heraga
Originally there were going to be two Multiperson Levels, this and Bowser's Castle. Low turnout on both lead to some rooms being moved over to here and the remaining being reworked and expanded on for Bowser's Castle. Even then, some rooms were taken from other sources (such as cancelled hacks in the case of rooms 1, 5, and 14) or done at the absolute 11th hour (such as room 11).
The boss is a reference to Boss X from Saga Frontier, who is the final boss of Red's route (and whose boss track plays in the fight, done by MasterLink and backported by Wyatt). The original joke was that Boss X's appearance isn't even expected in the original game, and can be seen as a gag of sorts. I originally was going to reference that here but as it turned out the Message Box fix patch that LM installs seemingly also makes issues with Sprite Tool and the OW in this version, so it comes off as
completely unexpected. The boss itself had a bunch of last minute issues too (which Meatloaf, ASMagician Maks, and SimFan helped look into) such as it having a 30% chance of softlocking the player if it flies offscreen incorrectly, but those were fixed. Also shoutouts to Eminus for the art as well, which was meant to look like a spriterip that was downsampled and Yoshi's Head was plastered over.
Room 10 was redesigned a few times, so the one ingame was actually a later version. Room 3, 4, and 13 come from original Bowser Castle rooms.
The designer for room 11 was the guy who organized Bowser Castle 1 from VIP6. He hadn't really hacked since VIP6 (besides a few levels in a tentative collab), but was really honored to contribute something they felt was similar here.