There still seems to be some understandable uncertainty about getting Ascension to work in BG2EE and what the issues may be. So below are some tips and fixes based on my playtesting and frustrations. After a great deal of tinkering and annoyance, I have got a smooth experience.
The Sendai not dying bug was fixed by either patch 1.3 or v30 of SCS.
The required files are:
Big Picture : http://www.shsforums.net/files/file/546-the-big-picture-v181/
This has the Ascension mod. The WEIDU version is incompatible with BG2EE.
This is important for reasons I'll explain.
Slayer form fix (attached)
This is to solve the bug where changing to Slayer form continues to drain your health after you change back. Not sure who produced this fix but thanks.
Throne of Bhaal pools fix (attached) (by me!)
There's a bug with the pools that give you powers in the Throne of Bhaal. They heal you but do not restore your spells as they're meant to. This fixes the issue.
1. Big Picture Ascension. This should be first on your mod install list. A minimal installation of Big Picture works best in my experience. From what I can tell, BP uses custom scripts for creatures that can cause all sorts of problems, eg disappearing monsters, inability to rest in areas, Sendai not doing anything., etc So I recommend only these components:
Big Picture, core component (required for most subcomponents): v181-b4611
Ascension for BP: v181-b4611
Improved Abazigal: v181-b4611
Improved Demogorgon: v181-b4611
Improved Gromnir: v181-b4611
Improved Illasera: v181-b4611
Improved Sendai: v181-b4611
Improved Yaga-Shura: v181-b4611
2. Whatever quest, NPC, dialogues, fixpacks (BG2 Tweaks, Spell Revisions, Unfinished Business, Arestorations etc), other mods that you like. Note that Unfinished Business has a "Restored Bhaalspawn powers" component. I recommend that you do not install this as it conflicts with the restored powers that you get from the Ascension mod.
3. SCS. I suggest installing this because of the problems I mentioned with BP scripts. Certain SCS components will override those scripts. So you don't need to install everything but will need:
Initialise mod (all other components require this)
Initialise AI components (required for all tactical and AI components)
Smarter Throne of Bhaal final villain
Give Ascension versions of Irenicus and Sendai SCS scripts and abilities
Give Ascension demons SCS scripts and abilities
4. Slayer fix. Backup the relevant file in your Override directory and then copy this into it.
5. ToB pools fix. Backup the relevant files in your Override directory and then copy these into it.
Hopefully this will work for all of you. Please note that there may still be issues with Longer Road and Wheels of Prophecy working together.