I actually view Geider's Improved Tougher Melissan battle a worthy challenge, but until the bugs are resolved ...

At any rate, one of the big obstacles for the Melissan battle is that she invoke Absolute Immunity and Spell Shield at will. A way around this is to upgrade and keep for this occasion any +6 weapons you find along the way, Ixil's Nail, Staff of the Ram, Ravager, etc. It works. Again, till the bugs are worked out ...

So here then is my inquiry. The upgraded Foebane swords description is that it is +6 against extra-planar creatures? Would the final Melissan, evolving into a demi-god and in control of an abyssal plane, be considered an extra-planar creature for purposes of the sword being able to bypass Absolute Immunity. It would sure be nice to able to use a one-handed weapon for the occasion.

Well, she sure sounds like extra-planar, though I'm not sure BioWare made her one.
I suggest using the upgraded version of the Carsomyr, which also is +6. Melissan is Chaotic Evil, which meens that the Carsomyr does an additional +6 damage to her. Carsomyr +6 also gives you 50% magic resistance, and dispels magic when it strikes an opponent.
Perfect for Amellysan. ;)

is this the ascension melissan that comes with the five and sarevok? i haven't been able to complete this battle cos i was soloing, but taking down the five damages/weakens her? don't think attacking her is useful while her allies are still there.

The weapons with additional energy damage are the best (Flail of Ages +5, Storm Star +5, etc).
Reminder: Absolute Immunity only stops attacks with a normal, +1,+2,+3 and +4 weapons.
+5 and better weapons function normally.

I thought that the Death Tyrant is a beholder, not an undead beholder, but it is destroyable with Runehammer +5. Interesting...

I thought that the Death Tyrant is a beholder, not an undead beholder, but it is destroyable with Runehammer +5. Interesting... Death tyrants are not supposed to be undead. You're saying that Runehammer +5 was able to use the undead kill on it. Does turn undead work on them as well? If this is the case, Bioware must have goofed again. :D