Amid the Big Baddies of Mordenkainen’s Tome of Foes, Zuggtmoy, Demon Queen of Fungi, seems a little out of place. It’s obvious that she was put there more to respect previous D&D lore than anything else. What’s her goal? To make subservient slaves out of infected people… Do we need Zuggtmoy at all (as something that embodies a concept)?
Check out the real deal:
That’s truly the stuff of nigthmare!
But, as Attenborough explains, cordyceps, despite causing insect hecatombs, have overall a positive effect on the ecosystem. Indeed, fungus is so integral a part of nature that making it “demonic” seems a bit too much, even for D&D.
Tellingly, neither the vegepygmies and myconids, two fungus-themed creatures, are linked with Zuggtmoy in any way (compare this with the drow and Lolth say) and are not even evil. The MM tells us that they’re both of neutral alignment: they don’t attack unless they are harassed.
These fungus creatures can easily be used in a silly way (Gygax’s Expedition at the Barrier Peaks) or in a much more creepy mode, as the incomprehensible so often leads to horror (VanderMeer’s books).
Personnally I would use some of Zuggtmoy’s regional effects (MToF), which are suitably creepy, whenever there is a large colony of either vegepygmies or myconids in an area. As for Zuggtmoy herself, I think she would be more interesting as a Lovecraftian Great Old One and as such, she would make more sense as an unfathomable warlock Patron.