Darker Side is a category which consists of collecting 500 moons to access the Darker Side Kingdom and getting the Multi Moon at the end of it as fast as possible. Timing begins when selecting "Start" on a new file and ends when grabbing the Multimoon in the Darker Side Kingdom. Buying more than one moon from any shop is banned, but there is a category extension which allows it. The fastest version for this category is 1.1 digital, but that version is banned because of its inaccessibility, making 1.3 digital the fastest allowed version.
The route for this category is very tightly knit. Almost everything has a purpose. Some small action at the beginning (For example talking to the taxi guy in Sand Kingdom) influences things later in the run.
The current route juggles tourist moons, peach moons, warp painting paths, outfit notification, hint arts, and achievement moons (which covers a decent amount of them, see the route document)
The community also made a powerpoint to help you navigate this long category.