Nightmare Night.

It's one of Equestria's oldest traditions. Or, it was before the pony tribes became divided hundreds of years ago.

Months after Sunny and her friends helped the pony tribes of western Equestria see the light about pony unity, the time of year approaches when Nightmare Night used to be held. Sunny sees an opportunity to revive the ancient tradition.

But how does an Earth Pony do something like that without scaring the bejeebers out of everypony?

With a musical, of course!

...

It's going to go exactly as you would expect.