The enemy in this film is the hillarious 'Smoo', a rolling purple mass that glurbs and bubbles across the countryside, covering all of Ponyland eventually (this stuff's great! Eyes comes to the surface, pop out, and are swallowed up again!). It's the job of the little ponies to find the supposedly mythical flutterponies to help vanquish the appiration (brought upon them by the toadlike witch-mamma and her two Laurel and Hardy-type daughters).
As a quest film, it's a joy to behold, bringing all the best characters of the series to confront strange new landscapes and amazing creatures on their way. The songs are great too, just the sort of thing a six year old will drive you batty singing all day! -- like babypony Lickety Split's duet with the pink dragonling Spike ("I'll go it alone") when she realises she's just not fitting in, and ends up on her own epic quest, meeting a cave full of funny little creatures that help her on her way, or the echoing-well song when she bemoans her outcast state, eventually realising that a flutterpony is stuck in the well and is asking for her help!
Megan's there too -- the veritable Barbie of MLP -- and her relations who might as well be Ken and Skipper, and she takes care of all the stuff that needs opposable thumb-usage.
This film will delight young people who've never seen it, as well as older people who have. ;) And the DVD format means that you don't have to deal with all that graininess and line-forming that we all remember from the 80s!