Per 
Ok, initial concept.
Type: physically inert item (haven't decided what, exactly, maybe a locket?) that "projects" a field of effect, with the radius growing in size if it's been too long since it last affected someone. Anyone that progresses into REM sleep within the radius will be affected by the item (only one person at any given time, although affecting multiple people at once could be interesting).
Effects: (trying to not write this too technically, I'll save that for the actual entry) Once the subject enters REM sleep, they will experience an extremely vivid dream, always of the same place. I haven't hammered out specific details yet, but it will be some sort of small country church, circa 1940s, set up for an outdoor wedding in a densely wooded area. Of note is that any physical injury sustained while in the dream will spontaneously effect the dreamer, with no cause visible to observers. Additionally, regardless of injury, the subject will not wake up unless they do certain things in the dream (which is generally how you get out/wake up) or are woken by external stimulus (which will result in something Bad, haven't decided what yet).
The entire area is hazardous in a fantastical sort of way, with things like Butterwort-esque gauze curtains hanging from a wedding pavilion, volatile/exploding presents on a gift table, poisonous hors d'oeuvres, and predatory flora in the remarkably dense forest surrounding the church. However, the focal point of the dream, and only other sign of human life in it, is the body of the "bride". She/it appears to be comatose when found, but if disturbed, will scream loud enough (140+ db) to cause permanent hearing damage, and will result in the subject waking up with full memory of the events of the dream.
Containment: The item can get put in a locker somewhere, but after testing, the foundation will discover that it periodically needs to expose a D-class to it to keep the radius from expanding too much.
Narrative/"hook":
