This is random, and maybe you don't remember this, but the top of the Succubus Tower in Lust Doll if you visit the top floor, two succubi tell you "sorry, you can't see the Queen". Lust Doll Plus, you are allowed to see the Queen in all her sham glory. Did you want to put the Queen as a character in LD and couldn't make it work, or was it something that didn't occur until LD+?
Given how the succubi act, I would think there was a secret area where the succubi are playing strip poker and the loser has to go around Transylvania naked with a sign that says "lousy at poker but still a hot succubus" or something...