Difficulty: Medium.

That's the name of the legendary black army that filled only dusty scrolls in the library in Canterlot years ago. Even princesses Celestia and Luna had no idea about this legend, which in a moment became a terrifying everyday reality.

After negotiations failed and war broke out, the whole country united against the blacks, but after centuries of peace, the current inhabitants of all corners of Equestia were not prepared for the beasts that are in their ranks and without a single victorious battle, they cower in defensive trenches.

The overwhelming defeat has nothing to do with the fact that the enemy have good training, much more advanced technology of weapons and armor, no, their power rises elsewhere and it gives them an incredible advantage over every enemy that crosses their path.
Even Princess Luna recognized this on her own skin after she protected the retreating army in a desperate fight, which despite all her power she could not save..................not even herself.

Now the scattered nations and Equestria slowly burned to ashes, the absent princesses and the last resistance defend with all their might the last few remaining territories.

Is there any chance of rescue?