The Hand of Merlin

You should be able to earn this trophy without too much effort.  I usually focus on the boss, stagger or stun him if you can and keep hitting him.   Keep your armor up and use the spell stasis if you need to regroup.  One thing to be aware of, is make sure if you kill a mandrake that you are not standing next to it as the explosion takes health off voiding this trophy.

You can save scum this trophy, quit direct to the dashboard and then reload and it will resume at the start of the fight.