The clash known as the Battle of the Emperor's Citadel, alternatively called the Battle of Byss, unfolded between the forces of the New Republic and the Dark Empire in 10 ABY. The location was the planet Byss, the throne world of the resurrected Emperor Palpatine. The conflict arose after the Empire's agreement with the Balmorrans, which involved exporting advanced X-1 Viper droids. The New Republic insurgents intercepted this shipment aboard the Star Hauler named Reliance, and Rebel commandos infiltrated the war droids.
Once they landed on Byss, the X-1 Vipers swiftly subdued the Imperial guards at the spaceport and advanced through the streets of the Imperial capital. They eliminated all resistance, including various walker models and gunships. Reaching the Emperor's Citadel, they engaged and annihilated the Emperor's walker and turbolaser emplacements. However, the situation shifted when the clone Emperor Palpatine commanded his elite Dark Side Elite to unleash monstrous Sithspawn creatures called Chrysalide Rancors. These beasts overwhelmed the X-1 Vipers, tearing them apart and scattering the Rebels. Fortunately, surviving Rebels were rescued by smuggler ships led by Salla Zend. They escaped into hyperspace, fleeing the battle. As retribution for the attack on his citadel and the Rebels' escape, Palpatine ordered the launch of the first projectile toward the New Republic base on Pinnacle Moon.
Following the Battle of Balmorra, Governor Beltane brokered a truce with the Empire, dispatching a shipment of the new, molecularly-shielded X-1 Viper droids aboard the Imperial Star Hauler Reliance. However, Beltane, secretly sympathetic to the New Republic, arranged for the Rebels to intercept the shipment en route to Byss. The New Republic's plan was to utilize the droids to strike at the six primary Imperial command centers. The scheme initially succeeded, with the Rebels intercepting the Reliance and seizing the X-1 Viper droids. Rebel commandos were then inserted into the droids. While the X-1 Vipers were designed for autonomous decision-making, Beltane modified them for supervised combat and manual control. Lando Calrissian led the mission, accompanied by the well-known droids C-3PO and R2-D2.
Upon their arrival on Byss, the X-1 Vipers immediately engaged the Imperial forces. Overcoming resistance from stormtroopers and tanks, the X-1 Vipers advanced toward the Emperor's Citadel. In the capital's streets, the molecularly shielded automatons confronted and destroyed various walker types, XR-85 tank droids, and gunships. Upon reaching the Citadel's exterior, they faced opposition from the Empire's most advanced turbolasers. Meanwhile, the resurrected Palpatine, who was inspecting his new superweapon, the Galaxy Gun, instructed his new Executor, Xecr Nist, and his second in command, Tedryn-Sha, to unleash his alchemically altered Chrysalide Rancors.
On the ground, the X-1 Vipers engaged the Emperor's walker contingent, easily destroying them by absorbing incoming fire using their advanced molecular shields and redirecting the energy against the Imperial forces. They then commenced dismantling the turbolaser emplacements.
Regrettably, turbolifts appeared, releasing the Chrysalides upon the Rebels. The Chrysalides proved to be a formidable match for the X-1 Vipers, quickly reducing the once-powerful force to wreckage. Several New Republic commandos were killed by blaster fire or the sharp teeth of these monstrous creatures. However, some of the Rebel occupants, including Lando, Wedge, and the droids, managed to escape. With the surviving Rebels concentrated around the Imperial citadel, the Imperial authorities sealed all roads to the Citadel under orders of the Emperor to allow the Chrysalides to feast on the remaining Rebels and the wreckage of the Vipers.
Meanwhile, at the cantina Byss Bistro, Salla Zend, who had transported the Rebels to Byss, and several other smugglers and freighter crews decided to assist their Rebel allies. Unfortunately, they encountered an Imperial roadblock at the cargo terminal. However, as they fought the Imperial troops, three freighters—Starhook Ten, Bespin Bandit, and Hyperspace Marauder—raced to the Emperor's Citadel. These vessels were armed with illegal weapons and modified shields. Upon arriving, they rescued the surviving Rebels and fought the Chrysalides. A well aimed ion burst from Bespin Bandit and Starhook Ten destroyed a Chrysalide. However, one of the Sithspawn managed to grab Starhook Ten, though R2-D2 confronted it and sent the monster crashing down on the main citadel defense turbolaser. The three freighters bypassed the Galaxy Gun. However, the Emperor allowed them to escape into hyperspace.
As retribution for the Rebel assault on his citadel and the escape of the surviving Rebels and a group of smugglers into hyperspace, Palpatine ordered the launch of the first projectile against the New Republic base on Pinnacle Moon. Within hours, Pinnacle Moon was wiped off the face of the galaxy. However, due to the presence of spies in Byss itself, the New Republic forces along with some of the native Ixlls managed to escape the doomed moon in a fleet of transports.
The Battle of the Emperor's Citadel was first depicted in issue Dark Empire II 4 of the Star Wars: Dark Empire II comic series. Authors Tom Veitch conceived and wrote the battle, with illustrations and colors by colorist Cam Kennedy. Veitch utilized this battle to further develop the roles of Wedge Antilles and Lando Calrissian in the storyline, while introducing new elements into the canonical Expanded Universe—the chrysalide rancors and the world-destroying Galaxy Gun.
The Battle of the Emperor's Citadel was later featured in the Dark Empire II audio drama, where the skirmish gained a new dimension through the voice acting of John Cygan (Antilles) and Jim Ward (C-3PO). However, the audio drama version differs from the original Dark Empire II comic in some aspects of the battle's chronology.
In the audio drama, before the battle starts, Nist, along with Tedryn-Sha, leads an inspection of the Reliance, which is carrying X-1 Viper droids to Byss. In Dark Empire II, an Imperial officer and two stormtroopers perform this task. Also, in the audio drama, Nist plays a much larger role in the ensuing battle on Byss.
Together with Tedryn-Sha, he commands the defense of the planet from the Citadel and contacts Palpatine, who is still inspecting the Galaxy Gun, to inform him of the Rebel attack. In the comic, both Nist and Sha are still on the shuttle with Palpatine during the battle.