Have you completed everything else in Broken Valley? Level 14 or 15 would probably be better for this stage of the game.
The scale is on the path to the blood alter, so you'll either need to run/jump to avoid Amdusias' attacks, or maybe use Hide in Shadows (you may have, or be able to find, that skill bonus on a piece of jewellery).
BTW when you finish off Amdusias you will get access to Sentinel Island. Your first encounter there you can mindread to go up a level, so the higher level you are (I made it to level 22 in the fjords) the more of an experience bonus that will be. You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus.
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