Thrust into a universe that is not his own Dusk Shine will find that being stuck in a diffrent world is the least of his problems as he clashes with previously banished Queen Chrysalis princess Luna growing attraction and his angry female counterpart
Starswirl's unfinished spell didn't swap marks. It merged destinies with other worlds where things happened differently. In a world where it all went wrong, only ponies from the world where everything went right can help.
Herds. In a world inhabited by magical ponies, that's really not too surprising of a thing... unless that herd consists of four living, breathing goddesses and yourself.
Myths and Birthrights side-story: Velvet Sparkle recounts her younger years in a nation north of Equestria and the events leading up to her becoming the mother of Shining Amour and Twilight Sparkle