What's worse than becoming a pony? I'll tell you. Transforming into Princess Cadance during a college class and waking up in a horse-trailer. Yeah. Life's screwed up.
Animale is a legalized drug that provides users temporary body modifications - have your own unicorn horn, ears, wings, for a night. Not to be abused. Ever.
Discord comes to Earth looking for fun. Unfortunately for one unlucky human, this means turning them into a pony and letting them loose into a convention.