The bug with the Demon of Lies not completing the death animation if killed by a trap or summoned creature should be fixed in the
patch.
There can also be a glitch in general if combining any two of Frost on a weapon, Stun on a weapon and the passive Stun skill, where creatures can hang in mid death animation. In those cases using an area effect spell that does not need a target, such as Hell Spikes, would force the animation to complete (some people also had them complete after a delay, or after their character slept).
If you still have a save with the overlord, you can try crossing the swamp with the teleporter pyramids.
Speaking of over-powered, there is a skeleton summoner in the catacombs under the warrior's guild, which starts summoning on sight of opponents and can build up a very large following. Someone posted in the old forum about this, and had a screenshot with the mini-map half filled with the green crosses of skeletons. Apparently the summoner does not have the same mana restrictions after being resurrected and subjected to Aura of Command, so can summon fairly fast.
With the Polymorph spell in Beyond Divinity, your chance of changing a creature goes up with the skill level, and it is possible to end up with a more powerful creature (I never used the spell, though, so don't know if it is effective on bosses).