This story takes place in the same universe as Temporary Rules and has been created with permission.
While watching over the kingdom for Twilight. Celestia and Luna have found themselves at the forefront of a war with a small army lead by three pony leaders who want to go back to the old days where the tribes are separate.
One pony, with his lackies, leads a small battalion of mechanical pony centurions through the Everfree forest. Drawing the attention of its guardian who chooses six mares to be his champions and deal this army it's downfall.