A changeling crash-landed somewhere near Ponyville after being thrown by the shock wave he had experienced back then in Canterlot. Apparently he is parted from his comrades and he's too far away from the Changelings' hive. Luckily for him, the Mane 6 rescued him in order to get information about those Changelings, hoping that they would find and execute the best way to deal with them.

...Mane 6 didn't know about his loss of memory, aside from his bad wounds by the time he was found.

As the stranded changeling awake, it's his new life he'll be continuing with the desire to know his past....