You need to find the ring in order to summon Cal, your friendly neighbourhood imp. Once you find it, you can summon him, and through dialogue, figure out just how many elves, humans, illithids, etc, you've killed throughout the game.
This only applies to the PC however. And, of course, the counting doesn't start until the mod is installed. Maybe later, if people actually like this, I'll incorporate the other NPC's, but for now, this is all you get.
You'll find the ring somewhere in the promenade, check the containers thoroughly.
You can download Cal here, and you can view the readme here.