XSUPREMEXSKILLZ
The Immortal Emperor
lemme just sum this up with an excerpt from swtor.com's forums:
I already know exactly what kind of statement is going to be made against this: 'he had enhancements' in the form of his Amulet and his gauntlets.
This is an assumption and not canon, those objects only quickened his corruption to the Dark Side, for a small amount of time they imbued his power, but afterwards their effectiveness dwindled till the point that at his corruption of the Jedi knights and padawans via a holocron, they did nothing for him and he wore them for aesthetics and intimidation factor only.
Exar Kun was very powerful and he did not require the aid of power imbuing objects to enhance this power, by the time of Ulic's capture at Coruscant, Ulic admitted no one person was powerful to face him directly, which is why the entire 10,000+ strong Jedi Order had to turn up and attempt to stop him.
Exar Kun was beyond his duelling skills most infamous for being able to attack someone or multiple persons with a blast of pure Dark Side energy, an energy that even the likes of Darth Bane had no defence against at all and he flopped around like a fish out of water when a Dark Side Tendril severed his arm.
Exar Kun was the strongest user of Dark Side energetic blasts on record, when Aleema Keto attempted to kill him with this ability he simply absorbed the blow and blasted her with a far stronger attack that Aleema only survived by shielding herself with a dark side force bubble that only took the brunt of the attack, it still knocked her unconscious.
Exar Kun showed his total mastery of Force Blast against Gantoris, using it via his eyes instead of his hands, totally incinerating the promising Jedi Knight.
Exar Kun was also a master practitioner of Force Flight able to move at will in a strain similar to Count Dooku.
Exar Kun's mastery of Sith Alchemy and Magics was nothing short of spectacular, he could easily create hosts of Sith war beasts including the dreaded Terentatek, eventually this power was so immense it allowed him to absorb the Massassi species and abandon his body. 4,000 years after this as a Sith Spirit Kun would have used the students of the Jedi Praxeum to rebuild his own body through his alchemy, essentially allowing him to move from the corporeal to the non-corporeal whenever he wished.
His Force Sense was also powerful enough to know his apprentice Ulic Qel-Droma was endangered from half the galaxy away.
Kun's duelling skills are also valid here, as his form relied on Force prowess to be used, he was the most powerful and skilled Niman user on record, taking it to it's highest form, he mastered it to such a degree that he could easily use the force to randomly turn one or both blades on and off mid-combat with no manual button, he could also do the same thing and change the length of each blade as he saw fit, as he gained esoteric levels of power in the Dark Side he threw any type of moderation or balance out of his lightsaber style and incorporated highly proficient levels of Juyo and Ataru(in the form of Force Flight), this was so powerful that masters of Djem-So Vodo Siosk Baas and Ulic Qel-Droma had to stay on the defensive and in one case was totally overpowered and killed(Baas).