The Tyrants and the Princesses - Imprisonment

Commission work done by *FoxInShadow, this one depicting the Tyrant Celestia and Luna from the 3rd 'series' of stories that I plan on writing (but haven't written yet!).

In my 3rd series I plan to write, the Alicorn Princess Twilight Sparkle is in grave danger and is in a coma. In order to save her, only the most powerful and fastest of Equestria (being the 3 Alicorn Princesses) can retrieve the items she needs in order to survive and make it back in time before it is too late.

The illustration above occurs when the three Princesses go to retrieve the 'Mirror of Truth'; however they fall into a Mirror-Universe of an alternate Equestria that is the opposite of the bright and shining one that we all know. There, the Tyrants Celestia and Luna (placeholder names) imprison them as there is no sun or moon in this Mirror World for the good princesses to get their powers. Will they be able to escape and return home with the Mirror of Truth before it is too late for Twilight Sparkle?!