Wandering about in the game spell list, I found a couple of spells with the "Selûne" tag.
If I am not mistaken, these are the spells used by Dradeel if you get to attack him on BG1.
One of them is Selune's Blade, basically a flaming blade, nothing interesting.
The two other, however, are interesting:
Selune's blessing, an instant cast, fairly long-lasting, -5 bonus to AC. Not quite that strong very lategame, but very interesting early
Selune's curse: a blue, magic-damage-dealing fireball with increased damage. Same behaviour with Save vs Spells, area of effect, etc... and it hurts party as well.
I thought these spells would perfectly fit in the two spells priest kits get, Curse once per ten level, blessing once per 5 level.
As for Alignment etc..., I would say either good, or Chaotic Neutral, based on Selune Alignment (She is Chaotic good).
I guess that's it for Priest of Selune. Priest of Bhaal now:
They usually are Assassin/Cleric, but I thought one could just give Poison Weapon to a Cleric through EEKeeper as one of the two spells they get, and give them uses of Hand of Murder (one of the abilities you get after pocket plane challenges) from level 10 (that s when it starts to do something). And ultimately, after having killed enough people in Slayer form, give them a Ravager Change (if it works. Enegar does it in BP2 but I did not check whether it works)