Zuggtmoy, Demon Queen of Fungi

Zuggtmoy by Marcel Budde

Zuggtmoy, known as both the Queen of Fungi and the Lady of Rot and Decay, is relatively straightforward as far as demon lords go. Whereas others make grandiose plans to achieve complex goals, Zuggtmoy's objective is a simple one: infect living hosts with her spores. Those infected by Zuggtmoy slowly lose themselves as they become one with her, the demon lady working through them as their bodies slowly rot until they decay into compost for the fungi she spawns. Though she frequently takes on a humanoid shape, there is nothing resembling a sound person's judgment lurking anywhere within her mind. Her very nature ensures that she has no allies, only servants who are ultimately little more than extensions of herself.
Most of her thralls come to serve her when unwillingly infected with her spores, but there are those few who come to serve Zuggtmoy of their own volition. Typically, these individuals are either utterly mad or falsely believe they will be able to maintain their sense of self while partaking in Zuggtmoy's power. Her only true enemy is the demon lord Jubilex, with whom she unwillingly shares a layer of the Abyss. Given that Lord of Nothing's nature is that of an ooze, most believe is it merely a matter of time before Zuggtmoy absorbs him or vice versa.

Shadows Unleashed Campaign

On Nexus, the Cult of Zuggtmoy thankfully operates with limited success. A small collection of mad druids is the only reason Zuggtmoy's influence extends to this world at all. Though they commonly sequester themselves in isolated underground areas, occasionally they come into contact with civilization. They very nearly caused an outbreak in the nation of Lothal around the time the local Adventurer's Guild was dealing with the Morlock threat. While one of their number was slain by the adventurer group the Headhunters, it was actually a member of the Morlocks, Moltor, who eliminated the bulk of the group on orders from his master Orcus, Demon Lord of the Undead.
Despite Orcus' usual lack of interest in Zuggtmoy, he wanted no interference from any other demon lords disrupting his cult's plan in Lothal. Though Moltor was partially responsible for stopping an outbreak of Zuggtmoy's spores from spreading (truly, this was mostly thanks to a controlled burn by the gold dragon Shimmerscale), this proved to be something of a mixed blessing for the people of Lothal. Moltor was able to steal the cults research and combine it with his own necromantic knowledge to create the Molders, giving the Morlocks a near-endless army of expendable foot soldiers.