The duel between The Paladin and The Iron Mark is one for both parties, as the King's Champion and the Lord of the Demons more than prove how they each earned their title.
The confrontation between Meeks, The Paladin, and the black unicorn at the end of (duh) The Black Unicorn is the highlight of the book. The Paladin slaughters Meeks' personal demon. Meeks summons an army of skeletons to battle The Paladin. Willow frees the black unicorn to attack Meeks. Abernathy frees the other unicorns leading to Meeks' defeat. Just great, fast-moving stuff.
Questor riding Strabo right into Ben's world to save him, Willow, and Abernathy from Michel Ard Rhi and his spurious lawsuit. Coming right on the heels of Questor's duel with Strabo, a CMOA in and of itself.
Strabo laying waste to the demonic army in Tangle Box, and slaughtering the wurm in Witches' Brew.
Edgewood Dirk matching Meeks and his demon in Black Unicorn and staring down Nightshade in Tangle Box.
The battle between the Ardsheal and the robot in Witches' Brew, is badass enough, but the subsequent fight between the undead, mind controlled Ardsheal and The Paladin is flatout amazing, lasting pages, and taxing both combatants to their limits.