well actually D CP, the ancient sith were gods, go read page two on the Ulic vs Revan thread for lots of info on the ancient sith, however, here is the info on Kun again:
Exar was an exceptional duelling master.
He also was able to freeze the entire (which had jedi that were in the building) with one spell and then rescue his apprentice and kill an extremely powerful jedi master and nobody could do a thing about it. This jedi master was also very similar to Yoda and been training for 600 years, also remember that the jedi master was training during the height or war in the republic so he knew battle better than Yoda did.
The jedi order also sent thousands of jedi to kill Exar. He was able to repel all of them long enough to preserve his spirit for thousands of years.
And Exar did study alot, Vodo-Baas says that Exar is the most powerful student he has ever trained and the most powerful force user of that time, and Vodo was similar to Yoda, he trained lots of jedi over a long period of time, and if Exar was the best, that means something.
Exar also studied alot, he was fascinated by the sith teachings in Vodo's holocron. Exar also learned under the ancient sith, like Freedon Nadd and Marka Ragnos, he would still be very smart. It is also worth noting that the ancient sith said that Exar would be the one to bring about the golden age of the sith and said that he was the Dark Lord of the Sith, over Ulic-Qel Droma.
Exar Kun was also able to destroy the entire massassani race, quite a feat. He drained their life force and used it to prolong his life.
His apprentice, Ulic, was a powerful jedi and dueller in his own right, but Exar was his unquestioned master and the ancient sith said that Kun would be the dark lord, not Ulic, this means that Kun is stronger than Ulic was.
He was also able to hide as a sith in the middle of the jedi stronghold (Ossus) and recruit jedi to become sith, without the jedi even knowing what he was doing, that's got to take some pretty impreesive power. He decived the best jedi in the order, took sith stuff and recruited new allies from the midst of the jedi ranks, lied to the jedi masters, and they couldn't even tell it was going on! Also, this planet (and its sun) were later blown up by Kun so anybody after him would have no knowledge of those things that Exar knew.
Also, he invented his own lightsaber, Exar was the person who invented the double blade lightsaber. He also designed his own unique style of duelling, something that he never tought to anyone and was lost after his defeat. So nobody other than him and Ulic had any idea what to expect from him (everyone else he faced ended up dead)
He is also an amazing dueller, after he decided to try against Vodo (a lightsaber master), Vodo died in around 10 seconds, before that Kun was just toying with him. Toying with him! In the middle of the senate chamber on the same planet as the jedi temple, he could still toy with one of the best duellers in the jedi order and win hands down.
Kun also learned loads of stuff from Ossus, which was later destroyed by him so anyone after him couldn't have learned anything from it, he also used sith holocrons and had the private notes of Naga Sadow, another sith who could blow up a sun. Naga was also a dark lord of the sith from 1000 years before Exar and was Marka Ragnos apprentice and had an amazing grasp of the dark side, Exar learned it all.
Kun was able to walk into the heart of the republic senate, freeze them all, kill their leader and a jedi master, and walk out, nobody could do a thing. This is in the heart of the jedi order! He was also able to kill a beast which is probably very similar to a terentek, or better, with very few problems. Exar was also able to walk into another jedi stronghold (Ossus), kill more jedi, steal the artifacts, and walk out again, unharmed. He was also able to destroy Freedon Nadd with no problems.
Think about how he died, he was faced against 10 000 jedi, and the republic fleet. Under those circumstances, anyone would have died. Exar died sure, but he was able to hold the entire fleet off with the force until he was able to figure out a plan to keep himself alive. Exar was able to kill off an entire race, numbering thousands, to keep himself alive, sure he was killed 4000 years later, but it still took 14 jedi, 12 padawans, Luke and Kuns old master to kill him. Think about it, 2 lightsabers, 12 padawans/knights, 2 jedi masters (including one of the most powerful jedi ever; Luke and the old version of Yoda, Vodo-Baas, he trained lots of jedi, for some reason I think of him like an old Yoda), to kill off Kun's 4000 year old ionized air particles! He must have been near godlike when he was alive.
When Kun walked, the ground shook underneath him from the shear power of the dark side emanating from his body.
Exar did invent his own style of lightsaber combat, the double blade, also, his double blade was different than any other double blade. He was able to move it faster and aim more than with other double blades. Also, since few people had never seen a double bladed sabre, it would throw them off. He can move his lightsaber so quickly that almost anyone he faced would be sliced before he knew what was going on.
Exar wore armor with a cortosis weave in it, allowing him to recieve hits from a lightsaber without doing him damage.
He was also a powerful sith alchemist and created several beasts.