Yea the black mushroom has been spawning since I believe the start of beta. I know I found some months ago. The difference is they used to only be a rare spawn right outside adrias hut, but it seems in patch 14 they changed it to spawn elsewhere. First day of patch 14 I found a spawn in the cathedral =)
Since you can't sell it, maybe either a future quest item, or an ingredient in something (maybe to whatever secret level I hope they put in =P )
The Black Mushroom is a Blizzard experiment to check the abilities granted to the search function in the forums. So far, it has shown that either the search function is broken, or that few know how to use it.
Being a scientist, I appreciate the subtleties involved.
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