Bowser in the Shadowy Void

Bowser in the Shadowy Void is an elusive course in Super Mario 64 reported to be a variant of the Eternal Fort, supposedly given to those who take the steps necessary to enter the Eternal Fort, but have only proven themselves to be almost worthy to enter.

Information
Just like with the Eternal Fort, information is scarce, but there is slightly more info on this course. This course is known to be a Bowser course, and usually involves traversing narrow platforms above a giant, shadowy void. Goombas have been reported in this course, alongside several sections involving precise wall kicks.

There are very few reports of Bowser in the Shadowy Void, and these only tend to be made whenever a discussion on the Eternal Fort is ongoing.

Speculation
It has been theorized that Bowser in the Shadowy Void was designed to be an easier version of the Eternal Fort, for those who wanted the challenge of a bonus, final level, but weren’t quite worthy for the real deal. Other theories speculate Bowser in the Shadowy Void was intentionally created, either by Nintendo or the Personalization AI, as a fake Eternal Fort to fool those who seek it, but were not yet worthy, however these theories have been widely disputed.