Tips for anyone running Lone Wolf Knight/Mage: (Normal difficulty.)
First, I did it at level 9, and reloaded a lot of chests/boss kills to make sure I got some pretty good gear for my trouble along the way. His opening round of attacks alone took both of my characters to 3/4 - 1/2 health and left burning. I thought for sure I would have to go level up more with how the fight started off, but once I got my crowd control rolling and healed up, the fight was pretty manageable. I didn't use any elemental shields, but a fire shield would make this a lot easier since two of them do pretty heavy fire damage, and use small fireball every few turns.
In order to do this at equal level as lone wolf you need the following:
Heals, crowd control, a decent sized HP pool. My knight has leech which mitigated some of the physical damage through healing.
Use knockdown/blind/stun on the summons and focus on one at a time. Heal as needed and keep buffs up as much as possible. My mage has 3 summons but I used none. They could be a useful distraction if your characters are taking too much damage for the heals to keep up with. Invis the mage if you need to avoid some damage for a round or two.
This is just one way of doing it, of course.