Need to kill a golem...

[Executor]

Disintegrate has longer range, so use that before opposition.
I see he has 23MR, that isn't good enough to keep him safe from repeated disintegrate so one will kill him if you provide enough chaff to work around.

But the best way to kill them is still magic duel if he forgets gems or teleport your own SC/Thug equipped to kill him.
Work on his weak points. He only has 12 protection, so for example use a thug with boots of quickness and gloves of the gladiator.