(From Professor Virgil Pendrake's personal research notes)
Unfortunately, my search has been lead awry. I originally set out searching for the Doomsday Mantle on hearsay that it was a very unique breed of mushroom, found to be growing near sites of great potential destruction, specifically between the hours of 12 am and 2:30am, local. This is the last time I trust any information dealt out by The Optometrist. In subsequent research, I have learned that this appears to be an item of clothing that has strong ties to 27, in that it is part of The Four Apart, and thus is an item sought after by most everyone poking their noses into this place.
As for the cloak itself, it seems to be an item of clothing that came into the possession of one Emanuel Stargazer not long before he died, though how this came about noone knows, as he was committed to a mental institution. (Cited through Eriek Flogger's article)
What I have learned, though, is that this cloak, wherever it is, must never be found. Upon questioning several locals, 3 ignored me, 1 threatened me with physical violence, 4 politely disavowed knowledge and walked away looking around like something was going to eat them, and a record 5 ran away as soon as I'd mentioned the item's name, one in particular yelling the word, 'Aethylwyne' over and over. I fear for the sake of this place should the Mantle become, 'unshrouded'.