I'd like to suggest another end for the bhaalspawn.
I never "obeyed" bhaal, but did side with him, I was going down this route of the bhaalspawn, not to appease bhaal or for some stupid evil playthrough, but because I chose to be a destroyer from the start, that's why I made the character.
If anything, I truly believe you guys channeled my conscious in the collective subconcious making this char.
The main dark urge before you start editing even looks like me in my dragon form in my mind, and not far off from the form I see myself as human, but more of a pale horned female humanoid with red eyes.
You see after I "sided" bhaal, basically to just say "yeah that was the route I was going anyway, I'm not gonna argue semantics" instead of being pettily obstinate.
Then chose to kill the elder brain, I didn't do it because I was defying bhaal, indeed I never really sided with him, or thought the elder brain was evil.
I did it for one reason and one reason alone, that using the elder brain is a too PUSSY way to destroy the world.
I can solo the damn game on the hardest mode and all my companions too with my build, and I could on bg2 aswell, I killed the elder brain because I wanted to murder it.
And all this sneaky control shit is cowardly and not me killing everything personally, me against the world, challenging the whole world directly.
So simply put, I killed the elder brain because I wanted to fight the entire world myself, and kill them all personally, on my own, with non of this subterfuge planning shit.
Just conquest by pure 1vAll strength, anyway, I suggest that be an optional ending, and if Bhaal isn't ok with that, he isn't worthy to be god of murder and is a fucking coward.