Moridin,
I'm not certain, but I don't think it's the same thing. I've never seen him knock an opponent backwards, as they always just explode into chunks of meat (200+HP damage in one blow). The other thing is that the dialogue box calls it "Deathbringer Assault", IIRC. Perhaps their interrelated, but I don't really know...
You're right though Larry...he does say "Die!" right before it happens. I never really put those two things together! It seems totally random...that's the weird part. I was planning on dropping Sarevok after a short while for Valgyar...but I don't think I can. I think that he's the best fighter in the game now...he's officially displaced Korgan in my book.
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Now where did I leave that doughnut?!