I finally had the chance to go back and watch the original My Little Pony Gen1 Pilot Rescue At Midnight Castle.
My memories of seeing this on video many years ago were that it involved black rainbows, ponies being turned into dragons, and the evil demon guy from the old Dungeons & Dragons cartoon.
Sadly, it wasn't QUITE as awesome as my childhood memories would have me believe. But it was still lots of fun and had some very non-girly elements to it, including dragons, beast-men, and a castle design right out of The Dark Crystal!
What was I saying? Oh! Have Firefly and the villian Tirek doing epic felt things!
Edit- I just realized my initial memories of G1 pony sounded like an episode of Metalocalypse. Which is awesome.