I don’t think I’ve ever used myconids, but that’s something I want to remediate soon enough. However, if I were to stick to D&D canon lore (which I won’t), myconids are supposed to be found exclusively in the underdark, the subterranean world home to the iconic drow. This was set in stone, so to speak, by Gary Gigax’s D1-2 Descent into the Depths of the Earth (1e), which of course, borrowed heavily on established hollow earth fiction (Jules Verne’s Voyage au centre de la Terre). More to the point, Gigax also borrowed the myconids, which were created in the earlier module  A4 In the Dungeons of the Slave Lords, which was an subteranean adventure (mostly) but in no way deep in the bowels of the earth-subteranean.

They belong on the surface!

Leaving the myconids out of most of the more typical (surface) encounters is both sad and needless, in my opinion. Put in any setting, the potential is just mind-blowing…