Until now it was the Gate District lich whom I've considered not to be the smartest lich ever to walk the earth - he usually manages to be killed by the pit fiend he gates in. In the meantime I've installed the improved lich from sola and our favorite undead should be tougher now. But obviously even an improved lich can commit proper suicide and doesn't even need a summoned fiend to achieve this.
Well, I suppose most of you know the lava pool in the shade lord temple, behind the first shadow door. If you enter the temple with high enough level (dc f15 / c17 in my case) you'll encounter a lich and some minions in the room north of the pool. I turned the minions to ash, but guess what the lich did? He stepped into the middle of the lava pool, obviously protected from anything on earth that could hurt - except fire - and gets fried, plain and simple. All I could do was run like hell to get there and hit him over the head with my staff to get the kill and the XP myself.
Thanks! My idea was that you don't get to 15 / 17 in chapter 3 if you start missing such occasions by admiring the scenery. I mean it was a lich (bad bad bad guy), so I thought I'd kick him while he's down.