Originally posted by Nephthys
Regular Force drain just siphons some Force power between the user and their target. Nihilus's variant completely drains the user of all Force, creates an absence in the Force, causes the user to become addicted to draining others and the hunger for force energy ravages their personality.Chris Avellone stated in this interview that the Ancient Sith knew about the variant that Nihilus and Traya used but didn't make use of it themselves because they didn't want to lose their personalities to the hunger. No other Sith who has used Force Drain has had to deal with this issue.
Also physically Nihilus' drain takes the shape of black smoke, whilst regular drain resembles red lightning in most cases.
Traya didn't loose her personality to the hunger, Neph.
Mr. Avellone's assertion have been overruled by BioWare:
The Sith Emperor, history's most powerful dark side master, performed a ritual of incredible scope to consume the life energy of every being on his homeworld.
Emperor consumed entire biota of his homeworld along with the Force itself surrounding the planet, leaving the planet as a void in the Force in the aftermath. In-fact, Emperor consumed the biota in such a manner that physical bodies of his victims no longer existed after the consumption. In short, Emperor surpassed even Darth Nihilus's ferocity in performing Force Drain.
Emperor would not have been able to perform this ritual without acquiring mastery in Force Drain and other talents, it represented the epitome of his Force Mastery in general. He didn't magically perform actions during the ritual, he prepared for this objective.
Also, KoTOR-CG pointed out that Nihilus performed Force Drain. He wasn't exclusive at learning this ability, Revan also did. KoTOR-CG revealed that Darth Nihilus mastered Force Drain.
Point is that KoTOR II and Mr. Avellone aren't the only sources to determine what Force Drain is, all available information should be taken in to consideration. This is what I have attempted to do in this thread but I have been accused of ignoring and other BS.
Darth Traya is a fallible character, she doesn't knows everything. She also lies and manipulates. She learned Force Drain as well but lied to Meetra Surik that this power could not be learned.
The actions of Emperor, Traya and Nihilus simply prove what can be achieved with Force Drain, if mastered to extreme level.
The analogy of Tutaminis explains this matter; Tutaminis based actions range from shielding skin from radiation of Sun to blocking a lightsaber with bare hands.
Their is no reason to assume that Emperor cannot be destructive with Force Drain in normal ways. He wouldn't have needed to grant immortality to his servants if he wasn't lethal with this talent.