Dragon Age 2: Act 2: Abandoned Thaig Nexus Golem take 2: Nightmare Level Mage.

Now with added potion tactics, and fixed Varrics screwed up Goads. Much better.
Claimed by some to be one of the most challenging encounters in Act 2 without resorting to cheese, thats hardly true. Ser Varnell, without cheese , is several magnitudes of order higher in difficulty, making this encounter a simple walk by comparison.