10. Fungus Queen - Pathfinder, PF2E
We've yet to come to the highest position for each type within our Mulch list (that being plant, ooze, and vermin) but we are now at what I would qualify as the top member of the subcategory which is fungus monsters. Which you know.... fungus isn't a plant at all. They're closer related to humans than to plants. It's probably about time we fixed that Wizards/Paizo. But whatever.
You may be somewhat familiar with Zuggtmoy, demon queen of fungus, who is a staple demon lord of D&D. While the Fungus Queen seems to be reminiscent of this feminine fungal power, Zuggtmoy is not an actual entity in Pathfinder and so it may be more intended as something of a replacement of the concept.
The Fungus Queen offer yet another faction in the "splintered" power structure of the Abyss. Now I leave that in quotations for a reason. The Abyss is always kind of a difficult beast to tackle in the cosmology of both Pathfinder and D&D. On one hand, its immensity and the details given for the myriad of layers and entities gives an untapped potential for storylines. On the other hand, there are elements of how the Abyss works that causes the internal politics of the plane and its inhabitants to be an intimidating element.
The large element at play here is that the many sections of the abyss are eternally turned against one another in an ever-changing struggle for power, with their only unifying element being their involvement on one side of the Blood War. This is all well and good as a concept, but unbridled chaos is a hard thing to just hand over to a creator without at least some sort of starting point of how to divide things up. There is so much in the Abyss to keep in mind whenever one is trying to construct something from scratch and so ultimately most stories that deal in anyway with the actual planar elements of it either A) Scratch the surface, B) Engage with it in the Blood War where the factions don't matter as much, or C) Touch on the few areas where there is a clear division.
Fortunately, the Fungus Queen serves as one of those clear divisions. It is with an opponent that already has a few of the known schisms but that's ok. The Fungus Queens are masters of seduction and, as such, hold a deep contempt towards the Succubus who vie for that particular role. They are themselves spawned from the corpses of succubus. The first were created as a spiteful perversion of succubi that attempted to kill a witch who held great power within Cyth V'Sug's realm, which is Pathfinder's fungal demon lord. Naturally, they take on a more wicked, natural, and coven-like roles than their original forms, making sure to keep peace with others of their 'harem' and take on territories of deep wild. Though they also retain much of their predecessors powers, twisted in new ways. Their kisses are even more potently deadly, with the chance to kill and fill these victims with their spores.
These then serve to extend their power as fungal zombies. However, as much as this assists to give them more influence (alongside other plants they can control) it does not seem to serve to extend their brood. This, ultimately, does require the corpse of a succubus. There does not seem to be another way that these creatures can spawn and so ultimately anything they do even in the Material Plane will also require them to be on the lookout for these potential egg sacs. These creatures are violently jealous though, and certainly this energy is just as like to drive them towards any other creature that might challenge their beauty, from Nymphs to Rusalka. I think this could also easily extend to the leaders of a forest town or even just a point of great personality and influence in their realm, such as a Green Dragon.
The Fungus Queen thus offers two points of potential conflict, both through presenting itself as a growing infection and influence point through its zombie and plant influence and also as a prominent social influence that quickly can turn violent against some other natural or supernatural force of charismatic influence in an area. I would personally strongly encourage the pursuit of both at once, which could give extensive combative and social ways to address the situation both with the other powers at play against and for the Fungus Queen, as well as the Queen herself.