I can take down the skeleton lord alright and the bone devils, its really just thessal himself and the way he keeps gating in more bone devils. I've tried focusing on killing him first but then his undead army becomes uncontrollable (i've had to face like more than like 7 bone devils at one point and some skeleton warriors) and the most i've taken him down to is badly injured before i die off.

This battle is primarily designed to be done in chapter 6. My guess is that you are simply low level for it.

Oh.... really i must be pretty good then, i've managed to get to the point where i've killed every summoned and gated creature he has but he himself (i've managed to get him down to badly injured before he stuns my character to death) is a tough nut.

thanks for telling me this otherwise i would have resorted to ... gulp cheating