Not replacing as in removing and putting something else in its place, but moving it to a different place.
The "Come Endless Darkness" plot is moving along nicely. But I really need to introduce the Temple of Elemental Evil at some point. I am now thinking of upping the HD of all the monsters and putting it into place right after the A series but before the GDQ series.
Which also brings up an interesting point. The characters in the current game are now 7th level, almost 8th. Goblins, in enough numbers, are still giving them a run for their money. More so than I recall 1st Ed doing.
If the big bad is Tharizdun in his aspect as the Elder Elemental Eye, what's Lolth's stake in this? Demons don't work together. Maybe through Ghaunadaur. OR maybe Ghaunadaur is manipulating events to get Lolth out of the picture. That could work. Ghaunadaur is nothing more than a puppet of Tharizdun anyway. Given that he is the God of abominations, then I could put him in the Temple prison instead of Zuggtmoy. It's an idea anyway.
Of course if he is in prison, how did he work out this long plan? Well maybe this is only the body, the mind has been roaming free. So if Tharizdun's mind or ego is trapped in Ghaunadaur's body. Where is Tharizdun's body? Well that is trapped in the lowest part of the Nine Hells. Sages call it Zargon the Returner. When these two meet then all Hell breaks loose. Though I think three parts is better. To cover the three evil alignments (Lawful Evil, Neutral Evil and Chaotic Evil), as a parody of the "holy trinity" and also (and more for me) as a representation of Tharizdun's Id, Ego and Super-ego. Zargon is the Id, Ghaunadaur is the ego and now I need a Super-ego, the one pulling the strings together. Maybe that is Tharizdun himself.
The Darkening of the Sun is not only beneficial to the Drow, Vampires and Mind Flayers, it is the sign of Tharizdun's return.
Sounds like a plan.