I start this discussion here rather than in "misc released mods" because the idea for this NPC is related to continuity as provided by BGT (or Big Picture, if you like).
It is a mod that starts at Candlekeep and even continues after the final battle of ToB (provided you follow the mods storyline along with your own).
The mod is large and requires a number of other mods (BGT and the megamods etc) to be installed first. It also requires you to start freshly from Candlekeep, thus it is aimed at the really dedicated players of the trilogy who like to discover something new and revisit the whole game again at the same time.
The main storyline of the Bhaalspawn is augmented by Sandrah's epic search for her own answers and contains numerous additional quests and hundreds of new Areas added to the game.
Another issue is an attempt to tie some loose ends of various parts and mods together and even.solve some contradictions in the original game.
Crossmod contents is provided for a large number of released mods throughout the trilogy. A list of mods that have been considered is available.
The download is here
Make sure that you take a look at the readme file to get an idea of the mod.
Cossmod list