Just for the record: when I first encountered that thing (right at the start of the game), I got one-shotted.How can I beat the first boss? Stone Watcher? It seems impossible
Now, I decided to try it again, just to see what could come of it. And I found out it was quite easy to defeat: I was just blindly swinging the sword, and randomly rolling back and forth (since the game runs choppy on my low-end PC, I could barely target the enemy). I spent only a couple of health potions (which wasn't really necessary).
The only loot was the Watcher's Eye.
I was lvl 8, with Legionnaire's 2-handed sword imbued with magic, in full Inquisitor's armor. I maxed up Health and Strength stats.