“Rainbow Dash didn’t like it, to have somepony masquerading as her, because she thought of herself as too awesome for anypony to pretend to be her. So when she got tasked to watch over the Changeling who pretended to be her before, who was now a Changeling form of herself, she always challenged it to a race every time she had the chance. Simply to prove how awesome she was, and how much better the original was over the imposter.
Changeling Rainbow Dash tried hard to keep up with the athletic mare. But even if it shared the same appearance as Rainbow Dash, it didn’t share her athletic skill and was always left behind.
One day Rainbow Dash’s mind was too far focused on her race. She increased the speed of her flying until the Changeling couldn’t follow her fast enough, where it disappeared from her vision. When she reached the goal and waited for it, she had to wait half an hour before this Changeling finally came back into her vision and reached the goal itself.
Rainbow Dash thought about mocking for its slowness, but then she realized that she had forgotten her supervising task and this changeling had actually left her custody several times. This Changeling could have used this opportunity to escape from her. But it never did; it always came back to her. Somehow, that made her realize that even a Changeling can be loyal too…
Her mind had now changed. Now, she wanted this Changeling to be more like her. She was going to train this Changeling to fly faster, even if it couldn’t fly as fast as her, she was going to make it become the fastest flying Changeling at the least.”