Battle of Mustafar (Astragon Uprising)

The Battle of Mustafar (Astragon Uprising) was the first battle where the previously unknown forerunners of the Astragon Empire made an appearance.

Prelude
This battle started during the Imperial Period, and by now the 501st had tracked a ship to Mustafar to destroy the last organized Separatist Holdout, the one under the command of Gizor Dellso (sure, there was a group of B1 Battle Droids that were left behind on and were never de-activated on Geonosis, but they never had any plans and were just "existing").

Gizor Dellso was a Geonosian separatist who was determined to continue the CIS fight. He discovered a previously hidded droid factory on Mustafar (when the lights are off, the rather drab-colored factory would've been missed unless you were on the hellish surface of Mustafar right next to it), and simply turned it on.

This factory cranked out his own private army of battle droids. These included assault droids, assasins, engineers, typical super battle droids, pilots, and marines. He discreetly gathered a small fleet of CIS ships that were probably hiding elsewhere.

He even was working on a sort of B4 Battle Droid that was supposedly going to ignite a new Clone War. He made two copies of the schematics, and he gathered many fellow geonosians to help him, who were still sharing Dellso's hatred of the Imperials.

The Battle, Part I
A single Imperial-class Star Destroyer emerged in orbit over the hellhole, and was greeted by an unexpected