Hence "nominal." He can suffer majorly fatal wounds like a lightsaber through the heart and people in the force will even *sense* his death, but he'll come back.
He's not as un-hurtable as Sion, but he can also use the power to kill others, which might do a number on Sion.
Registered: Apr 2011
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Sion's weakness isn't explored. It's apparent that he can hold himself together despite having thousands of fractures, and only his (completely confusing) affection for the Exile allowed his will to be eroded. Plot Induced Weakness aside, in a straight up fight I don't see Sion falling apart for anyone unless they really, really work creatively, like pinning him under a rock for example.
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When Galactic enters his ultimate BS pimp mode, they call him Marka Ragnos.
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That and the only places that Sion survived death were locations unusually strong with the dark side. (At least as far as I remember.) And Sion makes note of this in his confrontation with the Exile.
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I preface this with the casual admission that Wookieepedia does not a canon source make, but upon the possibility that the information is correct:
^^ This indicates that the medical staff could not determine whether or not Sion was dead and that he was placed in a kolto tank, which is known for its regenerative medical properties. I would consult ze videos, but I'm 32 minutes into a debate between Christopher Hitchens and William Lane Craig.
Registered: Apr 2011
Location: Hollywood, Hiding from fame
The holovid (Not Wookieepedia, derp) clearly states that the "thousand fractures" confound the doctor, and they say they cannot understand how "[his] body can stay in one piece". Obviously Sion is holding his jigsawed body together, kolto or no. And since kolto regenerates damaged tissue, I don't see how it actually helped Sion, seeing as he looked like Pinhead's ass for all his damage.
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When Galactic enters his ultimate BS pimp mode, they call him Marka Ragnos.
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It took me a while to find this, but beginning at the 18:54 mark, the medical officer is unable to determine whether or not Sion is dead. Given the nature of his state, it seems to fall more in line with a standard hibernation trance utilized by Jedi and Sith alike throughout the saga. I'd need to see the evidence of where he is medically dead and simply used the Force to reanimate himself. His dialogue throughout the game indicates that such a power is present solely when he is on a location strong with the dark side.