What do you do when you discover that a mistake you'd thought long fixed is still at large? If you're Twilight Sparkle, you bend time and space to fix it. With friendship, of course.
Bowser has another heinous scheme on his claws to defeat Mario and take Princess Peach once and for all, but the mushroom-eating plumber will have some help from six mares accidentally transported to the Mushroom Kingdom by a botched dimension spell.
A meteor impacts the nation of Equestria, Planet Equis. Tranquility is quickly snuffed out when a poison begins to spread violently. The Princesses cannot combat this unknown threat, as no knowledge of it exists. Help comes from an unexpected source.