I used a Death Knight. They weren't meant to fight it actually, being a 2 man party at 13th, Paladin and Warlock. It was just meant to be the guardian of the prize they were there to get, and they had the key to bypass it. But they decided to slug it out. I even had the Death Knight buff itself with +2 Elemental Weapon before the fight and assumed it had a Bless on it while carrying out it's duties. It won initiative and promptly dispelled the Protection from Evil on the Paladin so it could hit. Instead of casting it again Paladin decided to attack. I thought that was foolish and was looking forward to dishing out some sweet, sweet necrotic hits. The Paladin then proceeded to Crit it twice in the opening round with his flaming hammer. 1d8 Hammer, 1D8 Radiant, 2D6 fire, +6 for STR and fighting style, 22hp/hit on avg normally, and he didn't roll avg. Savage Attacker was a feat I wildly underestimated, especially with a character who rolls that many dice on a typical hit. He didn't even use smite and knocked it down to half hp. I forget exactly what the warlock did but he's no slouch when it comes to dishing out the hurt either. Death Knight got off its big blast spell, one round of attacks, and it was over.
Anyways, another story about how CR's can be misleading if you haven't really thought out how a fight is likely to go down.
