Equestria has been saved, all the important ponies have been saved, and through all of that the changelings have been reformed. With the exception of one.

As all the ponies escaped from their cocoon prisons they all see that the battle wasn't over yet once Chrysalis emerges from the rubble of her destroyed throne. They were all getting ready for the final showdown and put an end to evil tyrant's ways, however, once she emerged they all saw that something bad has happened.

Apparently the explosion the love from all the reformed changelings has caused was too much for Chrysalis to handle and in doing so caused the former queen to develop amnesia. Absolutely no memory of anything not even her own name.

Starlight Glimmer, however, sees this as an opportunity to make a new friend and she's willing to take the risk.