Princess Earth Pony by @digoraccoon (Diosden Rodriguez)

Loosely based on Disney's Emperor's New Groove. Luna was tired of always playing second fiddle and wished to take on the responsibility of running Equestria during the day. However, her sister never takes a day off, so Luna proceeds to force Celestia into a day long nap with one of Zecora's potions to give Luna her day in the light.

...it doesn't go quite as planned.