Darker Side is a category which consists of getting 500 moons to access the Darker Side Kingdom and getting the Multi Moon at the end of it as fast as possible.
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 and achievement moons (which covers a decent amount of them, see the route document)
Current Route Edit
The community also made a powerpoint to help you navigate this long category.