They say you give up a few things, chasing a dream. In those mists that's the literal truth, for every dream of yours that comes true, a piece of yourself, mind, body, or soul, gets taken by the mist. Worst part is, you won't even know what the cost of your dreams are until you go to leave, and by then you might not even have a mind left to change...
A fragment of the mists of creation, drawn to those desperate to make their dreams come true. Suitable for any magical fantasy setting.
It is rumoured that a sort of little people living deep in the green woods have magic acorns. If they throw and hit someone with by one of these acorns the victim will experience temporary madness for a small duration of time, making the babbling victim easy to capture of kill.