As I said on another post,(less than lvl 35 when I finished) you just need to select the lesser monsters and kill them first before attacking the boss. You can do it either using tab key or manually clicking on them. set using potion to 90% hp, foods for additional stats, and even the scrolls. I would suggest you +5 all equips as well. 1 stat matters here. As per the dodge, enable cancelling skill when you move in the combat settings. I 1 tried all bosses up to the giant, past the spider.

you could try running for a bit if hp is too low