Even though Vader died on the board of [i]Deathstar[/i] , he had yet to fully complete his destiny. By the grace of The Force, he was brought back to life in a foreign world.
Darth Vader, one of the most insidious villains in the entire galaxy, ends up in Equestria of all places. With no support from the Empire, this Sith Lord needs to find a way off the planet. Or he could take over it. Either one works.