Location: From Nen-i-Sul bridge 5e, s, open hole, d is his area.
Strategy: First kill the half-orc and get the pouch from his corpse - it
contains Necro key. Necro himself is located some north, behind closed and
locked door. Ways down before his door are dts! (Um, can anyone confirm this? I could have sworn all exits down before his door were a one-way exit from his area to the Nen-i-Sul area, with high climb percentage required. -Belamir) Once you go in, Necro will close and lock door, so make aliases to unlock/open to flee if you aren't sure that you can kill him! This door is nobreak/nobash, btw. No point for buffer to
attack him - skeletal warriors will rescue him instantly anyway. Don't nuke
skeletals - they will die at the same moment that Necro dies, and even if you
will kill them, Necro will summon new ones instantly.
Note that the skeletal warriors he summons are actually different mobs from the skeletal warriors that load elsewhere on Arda (as far as the trophy-system is concerned). So - it can be good exp to kill these. If you blind Necro and then bash disengage him, you can kill all the skeletal warriors you want (well, since it takes mana for him to summon each one, they aren't endless); after each one dies, just have a warrior bash disengage Necro until he summons another. Make sure Necro himself stays blind until you're finished with his warriors.
Warrior must just buff skeletals and rescue caster, caster nuke Necro. After his death, get ebony key from his corpse, unlock/open board and go e for his treasure. Then unlock/open grating and go out (down). Btw: board is noblock, so if you already have ebony key, no one will be able to trap you in here.
Note: Trying to solo the Necromancer is a very bad idea. After a short while he will become very upset and start instantly closing the door to his chamber when you try to open it. Instead of trying to spam it open and flee (which will not work), you must stop opening it for a moment or two - you will then be able to open it and flee without him instantly closing.
Level: Hero maxabsorb warrior + hero caster; very hard but possible for solo mage/cleric/shooting thief (nice link needed for solo). For cleric - blind him first.
Loads: Red amulet in pouch; fear scroll, fang and key for DK entrance (silver rod) in his treasure room in chest.
Mobs unique to the zone: