I'll get back to the mouths of madness in a bit. I'm in no rush. For now, it's back to the house above...
"The Invitation":
One of the PCs can't sleep at night. Ideally it's the one previously targeted by the house but it can be another just as easily (although you might lose that gaslight/group conflict effect if you start spreading too thin). Stomach pain/hunger/whatever is keeping them from restful sleep and they physiologically feel the need to move about the house during it's witching hour. This hour, that you as DM will determine, will have significance later on in the adventure.
As they wander about the house they will eventually interpret the pain in their stomach as one based on hunger. The kitchen will have probably already have been found at this time so off they go to fill their bellies.
Having satisfied their bodies they eventually return to their room/sleeping area. Yet before they extinguish their light source something out of the corner of their eye draws their attention to the mirror/writing desk. There, written with a steady, precise hand are the words "
I want to know, would you die for me too?".
As soon as the words register, a face/person appears in the mirror/corner of the room. It is the man who "approached" the PC in the scene "The mirror that tells no lies". This time his features are hardened, with an almost fanatical look in his eyes. He stares at the PC with burning, almost hypnotic eyes for a moment before suddenly vanishing, along with the writing.
If you want, lighten the man's appearance to benign and include the message "
I want to know, just what you could do". As we'll find out later on (through my version anyway) it's all relative.
In fact, for this particular backline I'll be providing two versions of this once-man: one for DM's who like charismatic challenges, and one for DMs who prefer to just unleash the dogs. I won't etch nothing in stone but I'll provide breadcrumbs for those two destinations.
As an alternative, use the old lady for one, the younger man for the other. I short-stroked my NPC intentions in an effort to hook interest from any of you who may be reading this.
And as to the question that nobody asked: Is there food in the kitchen, or not? DM decides. This could be a hotel/inn/guest stay encounter as well, so keep that in mind. If the PC keeps their food with their travel kit and their kit with them in their sleeping quarters then we can work with that too. Just sub in the return to the room with a turn around/whatever.