I have an addition to that Nyarlathotep idea. You know how he's a messenger for the Outer Gods, the whole heart and soul thing aside? Well I was thinking that he could be a representative or agent of sorts for the eldritch community as a whole in this RP. Like their senator on the Council so to speak. Furthermore, if you wanted to maintain his cosmic nature but keep the power levels on the lower end of the scale, I could also just say that he goes about his business on Earth or wherever we are using one of his less powerful avatars. That way he can not only have weaknesses, say to things like Elder Signs if you want to bring those into the mix, but also abide by a code of conduct laid out by Dracula possibly. We could also say that the stars aren't right so he has to send tiny fragments or avatars of himself, thus explaining his limited power.

I mean it's what he does in Mythos canon already anyways, so I could see that working here as well. But I can write him just as easily without the above idea as I can with it. Either way is fine by me. Just thought I'd spitball some ways to make that category of creature work while also giving potential in-universe reasoning for it.