Look at what Harald is doing with magic in his house rules for World of Darkness.
And how about those concepts in making a polycosmos work? The idea belief makes a thing more possible and disbelief less is a way overlapping planes could be separated.
The take on ghosts as the dead who don't accept is familiar, so how about the idea of ghosts as beings who do? They want to believe we're here and so, increasingly, we are.
Could that be a horror story for Flash Fearsday? Here's my 140-character effort.
I woke. They stood there. Aliens?
They looked me over, smiled. "You are real," they said. "We made you. And all you know."
"Let us play."
Is it more of that gamer horror? You can try at Lunching on Lamias too. I still haven't written anything for Jennie's Expansion Joints this week, but I'm getting there. You?