My first encounter with the alieness of the dungeons of B/X & Advanced Dungeons & Dragons first edition came in the form of Mike Carr's B1 Insearch of the Unknown. The fungus garden within the module was stocked with Shriekers, Violent Fungus, & tended by Myconids who owned that room. My uncle was DMing and it was back around when the Monster Manual II had been released.
Full-page advertisement for module B1 "In Search of the Unknown" appearing in The Dragon #s 22-25 (February-May, 1979) from the OSR Grimoire blog.
We'd been through B1 before but hadn't explored all of the ruin and there was something slightly off about the ruin at this point. The monsters were getting weirder as anti nature of the dungeon started to take over the ruins of B1. The underworld of the dungeons of Greyhawk began to infiltrate the ruins of Quasqueton . And it was during this time that we had a meeting with the Myconids as they were flanked by Vegepygmies as bodyguards. And we found out that it was the Myconids that were introducing shambling mounds, phantom fungi, assassin vines and roperlike plant monsters
And even when the adventurer's were absent the dungeon continued to attact monsters and other horrors to it. Even when we weren't playing my uncle as the DM was playing with and tweaking the dungeons of Quasqueton.