I have used it. It was in a published adventure in dungeon though. (The one that used the maps from the DMG. Monastery of the Fire Opal or somesuch.)
Never deliberately placed one.
The_Gneech said:
Well, I think you may be pointing at the problem right there: the creature was created to fill a metagame need.
I think herr Gneech hit it right on the head.
When I am designing monsters, I only very occasionally think about "filling a niche of a low level invisible monster." In short, you have designed to a criteria that I don't *typcially use.
When I design adventures, I think more of themes and logic within the game. I might use the Phantom Fungus if I had a plant-themed adventure, or had a fungus covered cavern, but that's about it. I would almost never have the goal of "this low level party needs to face an invisible creature." (If I
were to have a plant of fungus themed adventure locale, it would be a nice, flavorful addition to the same. But to date, I have no desire to do so. Though I guess whoever wrote the "plant consipiracy" section in
Touched by the Gods thinks it's a worthwhile theme.)
My upcoming games will feature dragon-worshipping sorcerers and flesh-shaping mind flayers. All of the follow on encounters, other than random encounters in transit, will be built around what sorts of creatures would associate with, serve, or be found around such creatures.
* - I say typically, because on occasion, I like to give specific characters a chance to shine. Like a paladin/sorcerer in one game who I perceived as weak, had true strike plus his normal combat abilities as a schtick. It wasn't a great tactic, but I conceived a situation where hitting a high AC -- in this case, an amulet on an otherwise invulnerable villain -- was important.