Twilight finds an ancient spell, she uses it, and most of the mane 6 get sent to the human world, and due to the spells "eccentricities" they are now stuck to the perimeter of a car, and only the car's owner can see it, and chaos ensues when some car guys start seeing pastel ponies out of nowhere.

edit 2018/07/10: changed rating to teen because I'm not sure if the violence in it is too serious for an everyone rating, btw it's not extreme violence or anything like that.