Every so often, I've mulled over the idea of a MU* setting where it's "modern gothic-horror" (vampires, were-things, etc..), but original system; with the "the supernatural isn't entirely hidden" aspect of Anita Blake: Vampire Hunter, but not actually AB:VH.
Instead, it'd be nice to take bits and pieces of various similar genres (be they RPG genres, tv shoes, etc.. WoD, Buffy, Dark Shadows, X-Files, Harry Dresden, Anne Rice, Charmed, etc.. lots of things lend itself to it), with an eye on what'd lend itself to a MU*. For example, Anita Blake's split between normal/alpha shifters and normal/master vampires seems to be rather unfitting, WoD's supernatural-bias also seems unfitting, Dark Shadows' "Were-things see a pentagram on the forehead of the person they'll kill next full moon" is in the same problem-boat.
So when it comes to "supernatural physics" (how is a new vampire made? Does garlic work? Does running water do anything? What's up with their reflections?), which bits seem like they should be avoided and which should be embraced?
For those unfamiliar with MU*, imagine a normal tabletop game where the DM/GM/ST isn't there 90% of the time. Or imagine some odd mix of a chat-room or forum RPG and a LARP. In those (really bad examples), there obviously isn't always going to be a moderator-type person for most matters of conflict. Also, the demographics tend to lean towards about half of the character-base being non-supernatural human-types, so some hand-waving, "Sure! Your vampire just zonks normal folks' minds! Let's not worry about the stats on the human-side of the equation!" affair really doesn't work out.