My guys are level 15 same as him and managed to take him down easily. No need for gimmicks or anything else. He took my glass cannon Jahan down to 30% HP but everyone else was topped up all the time. Not sure if I have such good gear or what but there hasn't been a challenging battle in ages.
Fortify/earth shield/summoned minions are your friend!
Are you talking about Divine Divinity (DD) or Divinity : Original Sin (D:OS) ?
