Yup, if you want to kill a passive mob, just run behind it and then poke it with mortal blow :)
Btw you also have a higher chance to land a critical attack on a normal swing when you stand behind the mob. So when you play in a party, try to position yourself behind the mob when it is attacking somebody else.
Hehe backstab ftw, that clears up a lot though :) but ill be soloing or duoing with a mystic a lot, and she doesnt make a very good tank :P but good info, ill keep it in mind!
I use a dagger exclusively and seem to have a much higher success rate using mortal blow.
Back: 70%
Side: 40%
Front: 40%
If you can't get a shot out at the backside do not open with mortal blow. Open with regular attack and then use mortal blow. The mob's defences seem to drop a bit after they fend off smaller stabs and that is the time to strike a good critical hit. Opening to front side of the mob does seem to fail about 90% of the tme. However waiting that extra two seconds seems to up the success rate by a factor of four.