The Assault on Mount Tantiss, also known as the battle of Mount Tantiss, was carried out by agents of the New Republic to shut down Grand Admiral Thrawn's cloning facility at Mount Tantiss on the planet Wayland.
The Mount Tantiss.
During the Thrawn campaign, former Emperor's Hand Mara Jade was arrested by the New Republic for a possible implication in an Imperial raid on Coruscant. She later revealed to Luke Skywalker that she knew the location of Thrawn's cloning facility. Skywalker agreed to liberate her in exchange for the coordinates of Wayland.
Meanwhile Imperial Colonel Kleyn Selid had discovered that Joruus C'baoth had killed General Freja Covell in manipulating his mind. Selid reported to Grand Admiral Thrawn, who ordered C'baoth to be put under arrest and confined in the Emperor's throne room. But, the Dark Jedi had the time to send Covell's forces to kill the ysalamiri placed by Thrawn near Mount Tantiss to control C'baoth.
On Coruscant, Leia Organa Solo met the smuggler Talon Karrde. He revealed to her that the Empire took a large amount of ysalamiri on Myrkr and that it could be a trap for Skywalker. They decided to go to Wayland together to warn their friends.
Ekhrikhor introduces Luke Skywalker to the Psadans and Myneyrshi.
Jedi Knight Luke Skywalker, along with Mara Jade, Han Solo, Chewbacca and Lando Calrissian landed on Wayland and trekked through the forests of Wayland to Mount Tantiss.
They first met a group of Noghri Death Commandos who came to Wayland to help the son of Darth Vader. They later met some inhabitants of the planets, the Myneyrshi and the Psadans, and convinced them to stay neutral. Some Myneyrshi eventually decided to help them in fighting the Empire.
Mara Jade fighting alongside Skywalker.
They eventually entered the Mount Tantiss facility when they fought stormtroopers. Calrissian and Chewbacca went off to find a way to destroy the facility while Skywalker and Jade went to look for the facility's remote destruct control. In the cloning chambers, Calrissian was eventually able to rig an arhythmic resonance scheme to destroy Mount Tantiss. Meanwhile Skywalker's sister, Leia Organa Solo, entered the facility with Talon Karrde.
Luke Skywalker duels his clone.
Skywalker and Jade entered the throne room and confronted the mad Jedi clone Joruus C'baoth. C'baoth killed the Force-dampening ysalamiri and revealed Luuke Skywalker, a clone of Skywalker. Skywalker and the clone faced off as C'baoth incapacitated Jade with a blast of Force lightning.
Eventually, Leia Organa Solo, Han Solo, and Talon Karrde entered the throne room. C'baoth unleashed a Force scream, stunning everyone in the room. Taking advantage of the Jedi Master's distraction, Jade managed to Force pull Organa Solo's lightsaber, and slew Skywalker's clone, carrying out the Emperor's last command. Enraged for the death of Skywalker's clone, the Jedi Master began to bring the ceiling down on Jade and Skywalker.
Mara Jade kills C'baoth.
However, Jade used Organa Solo's lightsaber to cut holes in the floor so that the rocks fell through and moved against C'baoth. Guided mentally by Organa Solo, she reached the insane Jedi and cut him down with the lightsaber. He exploded in a blast of dark side energy.
The destruction of the Mount Tantiss facility halted the Imperial cloning operation once and for all. With the death of Thrawn at the Battle of Bilbringi, the events of the day were disastrous for the Empire and ended the Thrawn campaign.
Skywalker's duel with his clone went on to traumatize him for the days following.
After the destruction of Mount Tantiss, Wayland became a planet of particular interest to the New Republic. Researchers and Intelligence officers scoured the planet and ruins for clues to aid in their defeat of Imperial warlords, discovering evidence that would lead to the political fallout of Bothan involvement in the destruction of Caamas. The New Republic also relocated the Noghri to the colony of New Nystao on Wayland to escape their collapsing home world of Honoghr.