As of 7/5/2016 there are three new folders, which are shown in green.

Kin- Stories where Sombra and Luna are related either as siblings, cousins, or something else. No shipping is allowed here.

Student and Teacher- This folder does not require them to be romantically involved, instead put stories here where Luna and Sombra are a student and teacher. It doesn't matter which is which so as long as they have that kind of bond.

Faustian Bargain- Stories where King Sombra helped create Nightmare Moon, knowingly or not. Shipping isn't required for this folder.

In which they are friends- Stories where these two start out or remain close friends. They must be main characters and if the story does start shipping them please put it in the Mane Folder.

It's Personal!- Folder for stories where hatred/rivalry between these two is focused on. They can also be bitter foes as long as they are at least secondary characters in the story. Stories about Sombra's banishment can go here as long as Luna is a main character as well and they interact with each other even if it is just trading insults or something like that. Themes such as betrayal are also appropriate.

Mane Folder- Yes, I know how bad a pun that is. This folder is for the bulk of the stories in this group, where King Sombra is shipped with Princess Luna.

Mirrorverse Sombra/Luna- Stories where Princess Luna is shipped with Mirrorverse Sombra. Or where King Sombra is shipped with Mirrorverse Luna.

Nightmare Moon- Stories where King Sombra is shipped with Nightmare Moon.

Romeo & Juliet- Stories where these two are depicted as star-crossed lovers of a sort, one of them meets ill fate, etc.

Ahoy!- It might have shipping but we can't be sure. Implied, unconfirmed, or probable shipping. Don't try to put stories here if you think there's Lunbra if you look hard enough. Instead if you spot a story that might contain this ship, ask an admin to put it here.