Long ago, Star Swirl the Bearded worked on mirrors that acted as portals to other worlds. After his return, he has revealed the extent of this study to Twilight and friends and asks them to fulfill the dying wish of his long-lost companion.
Twenty-five years ago, Amber Lily was left at the Ponyville Orphanage by her father, Herb. After two and a half decades of mourning his wife's death, he returns to Ponyville to find his daughter.
Phobias are something that every sentient thing must cope with. That does, of course, include a certain cast of pastel-colored ponies from another universe.