This is likely the hardest boss encounter in Awakening, with the exception of the Mother. The inferno golem is highly resistant (maybe immune) to fire damage, hits very hard, has several area of effect abilities, and is accompanied by the Lost, who is an adept spellcaster. Focus-fire the Lost first, since he has lesser defenses and his spells are a serious threat, and manage your characters to move out of flame patches as best you can. You can use either one or two tanks here, as with good gear and talents one warrior should be able to survive both bosses' onslaught without too much trouble. Also, utilize the waterfalls. They can put flames out and protect you from the golems fire attacks. Try running from one waterfall to the next while the golem is attacking you.After the Lost dies, nuke the inferno golem. Utilize cold damage and armor-reducing effects in particular, and note that the golem is immune to critical hits and backstabs. If you have two mages who have the spell Force Field, you can keep the inferno golem locked in place while you kill the Lost. The inferno golem will move one or two steps before the cooldown on the next mages Force Field has worn off. While fighting the inferno golem, if by any chance one of your mages gets targeted and pursued, run around with him in circles around the golem while the rest of the party nukes him. He is very slow and should be unable to catch you. See: Dragon Age: Origins