I can tell you with certainty that the sith spirits on dromund kaas and those around the galaxy are more powerful than a lot of living jedi/sith throughout the mythos. I can tell you that Darth Kallig, who was a contemporary of Tulak Hord, was uber. I can tell you Darth Thanaton has some ridiculous force powers.
Tell me about Darth Kallig and Tulak Hord, if there's any information. And anything on what Teneb (Thanaton) has done, as well as what happens to him, please. He was the main character of one comic miniseries
Kallig was the main rival of Tulak Hord and was actually killed by him. He was buried in the dark temple. Yes, the one that was built 2,000 years after his death, don't ask me how that works. He spends his time killing anyone that comes near his tomb. Darth Thanaton is a dark council member and he kicks your ass with some pretty sick force techniques. To defeat him, you have to learn how to force walk, which involves binding powerful sith spirits to yourself and gaining their powers. You learn this power from Darth Andru who is also in the dark temple. One of the sith you bind to yourself is Horak Mul from the GAOTS comics, on Hoth. Sadow had a temple made for sith assassins over there. But yea, Thanaton is very powerful, as is the spirit of Lord Kallig.
Yes, you kill Thanaton but only when you find a cure to the power you got with the force walk. Too much power too fast started killing you. Andru is a force ghost that you incorporate and then release when you kill Thanaton. Horak Mul apparently wasn't a joke either since they say he was killed by 5 of the most skilled sith assassins in the sith empire.