Since willpower isn’t used much, another spell based monster might make it worth thinking about putting more points into. The minor succubus would basically be a weaker version of the boss of floor 2, but instead of making you attack yourself when you’re hypnotized she could use weight gain spells on you. After making you gain a set amount of weight she would lose interest in you until you cross her again.
After you beat the Black Succubus she reveals that her sisters are much stronger than her. For plot purposes I won’t be making minor succubus monsters since the only other succubi will exist as bosses on the higher floors. There will be other monsters that use debuffs though which is what the Willpower stat will be useful against. Additionally when I release classes I will be including a class called Manipulator which deals in mind control and manipulation of the environment. Manipulator’s skills will scale off Willpower to give it more of a use.
I also agree with Cryptic here, if the succubus was a one-time boss I guess it’d be interesting to have smaller succubus monsters in one particular floor, but if she has sisters it’d take off interest.