It has been 5 years since the problem with the Sirens in the human world. However, Diamond now returns to Equestria to take care of a little unfinished business. Unexplained and ancient evil threatens the following: Planet Equis, Planet Triforce, Planet Mushroom and of course, Planet Earth, AKA the real world.

Diamond must team up with heroes from the troubled planets in order to take down this mysterious evil and save not only Equestria, but the entire universe from whatever is going to come down. With Diamond's tech mostly out of commission, it's not going to be easy this time around.