okay, i got this case idea from a series of videos called the phoenix wright/ mlp cases, but i have switched it up a bit and i believe that a case like this would work well... but please, watch the videos before continuing. its a great series.
the case goes a little like this.rainbow was planning on entering a race. however, dash is a main suspect for the murder of a mystery racer, whom was supposed to be her main competition. rainbow and this racer were planning on racing in the equestrian 500, a 500 mile race through... well... equestria.
the body of the victim was found in the everfree forest, charred by a thunder cloud just over the scene. this cloud had rainbow dash's hoof markings and was reported missing from the weather factory.
rainbow says that this mystery pony was black-mailing her, and she wanted payback. she just wanted to scare him. but is that the truth? could rainbow be playing a prank, or just be a cold hard murderer? nopony knows... yet.