The third boss was the easiest to me, just be sure to have a slowing weapon and keep hitting it without getting struck by those deadly cleavers; the fruit thrown at you lets you rage every time it comes to the edge of the platform. You can also dodge the second boss' charge by high-jumping it.
Too easy with a mage with only intellect... Just get "lightning touch", one of the base spells and then the third row electric one to hit more than 100... (with lightning mastery at level 10) That Obliterator 9000 didn't even attack me .-.