Its worth looking at the speed you can cast the acid spell, as well as your max distance. I found it difficult to kill Javings at first (doing that same mission). I amended my acid spell to give max distance (50 meters) with no time penalty. Even if this means a weaker spell you should be able to hit them 3-4 times before they come close enough to hit you back. Then build up the damage part of the spell as you level up and you will be able to kill them before they can even reach you.
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It's bad luck to be superstitious . . .Palta e decata, nan nec ilne matala.
When one goes on a journey it is not the scenery that changes, but the traveller