Too scary for their target audience
I just took my 4 year old daughter to see this today. I usually check common sense media before we see a movie, but I didn't think I would need to with My Little Pony since she watches the show and it's so innocent. Boy was I wrong! As other people have said, it was way too scary. I think the target audience for My Little Pony is probably 3-5, and I think the movie is way too scary for that age group. My daughter said several times that she didn't like it and wanted to leave during the scary parts, and there were lots of them. The funny, cute, happy, and sweet parts (what you'd expect of My Little Pony) were few and far between and definitely overshadowed by the sad, mean, and scary parts.
I did like the music. And at the end my daughter did say she liked it, but I'm not sure we'll ever watch it again.