What's the difference between these two tags? Should they be merged?
I think we should change friendship-is-magic to my-little-pony-fim. My Little Pony (MLP) is a long running franchise with many series under that banner. My Little Pony: Friendship is Magic (MLP: FiM) is simply the latest of these. It's conceivable we'll get MLP questions that aren't FiM questions (admittedly I'm not familiar with previous incarnations, so I can't speak to whether or not there are good questions to be had from them), but all FiM questions are necessarily MLP questions.
So deleting either one and creating a synonym would prevent proper tagging should there be non-FiM MLP questions in the future. It's similar to the family of star-trek or stargate where the various series have their own tags, then there's also the franchise tag. We just don't have the same wealth of fandom here for the other My Little Pony series that we do for the various Star Treks and Stargates, so the MLP tags' overlap leads to a terrible Venn diagram of 100% overlap.
I think the easiest solution would be to change friendship-is-magic to my-little-pony-fim. By using my-little-pony-fim, the My Little Pony questions are still easily identified, and we can eliminate having to use two tags to make up for a length limitation. For those 15 questions, they don't need a my-little-pony tag, because they're just about the show Friendship is Magic. If there are questions just about MLP beyond the scope of the current show, then my-little-pony would be applicable.
Edited to reflect Pureferret's suggestion for easier identification.
Regardless whether there are additional series in that universe, there are no questions here. This tag clutter doesn't help anyone. Since the tags always coincide, and 15 questions is a decent amount of variance, I'd vote to merge the tags into my-little-pony-fim (as suggested by Kevin and Gabe Willard) and leave the old tags as symlinks.