When Sunset sees herself as an alicorn in a magical mirror, she goes looking for answers, eventually going through the mirror into another world. Some things are better left alone though, as she finds herself trapped in the other world as a child.
Thorax is not the first Changeling to reform his hive... but all hives who have done so in the past have been cursed to extinction. Celestia assigns Daring Do to find out why, and stop history from repeating before it's too late.
Rainbow Dash is the best. Top of her class, envy of her peers, she's really living the life. Except she must not be good enough yet, because they still don't notice her.