Scion of Zuggtmoy

Scions of Zuggtmoy are a fungus-based Tanar'ri (well, a demon, at least) that serve in the armies of Zuggtmoy, the Demon Queen of Fungus. As you can probably guess from the name. They are a late addition to the ranks of the Abyss, being created in the Demonomicon splatbook for Dungeons & Dragons 4th Edition.

Created to serve as expendable cannon-fodder for Zuggtmoy's forces, the Scions are former demons captured by those loyal to Zuggtmoy and buried alive in one of her profane Gardens of Rot. Here, they are consumed by virulent abyssal fungi, which devour the demon's soul (well, what passes for a soul amongst demons, anyway) and eventually heaves them out of the sodden earth as a grotesque amalgam of fungus and undead fiendish flesh. But these plant-demons don't just look like fungus-infested zombies; they act like them too! Scions give off infectious spores which can take root in the flesh of mortals and demons they kill, devouring the lingering spiritual energies and transforming them into new scions. As a result, not only are these fungus demons found serving as front-line troops in Zuggtmoy's armies or guarding powerful cult priests in the Material Plane, but bands of them can be found wandering in the Abyss or even in the desolate reaches of worlds touched by Zuggtmoy's cult. This infectious aspect greatly pleases the Demon Queen of Fungus, who regards the scions' fecundity as integral to her desperate plan to ascend in power.

One of the stranger aspects of the scions is that they can manifest in different forms, based on the dominant personality attributes of the host-victim. The Demonomicon 4e contains rules for three specific scion variants:

Overgrowths are created from the souls of victims who were renowned for their tenacity (or sheer hatred), and when not ordered by a superior, they often hunt victims based on their murky memories of those they hated most in life. Appearance-wise, they're basically tentacle monsters made of slimy, oozing fungal branches and pseudopods, and the have the ability to induce rapid-growing parastic fungus as a weapon to bind victims in place.

In contrast, Infectors were created from the souls of cowards and deserters, and still retain a fundamental timidity. Bloated with corrosive spore-laden slime, whilst they can lash out at anything that draws too close, they prefer to pelt foes from afar with exploding mushrooms and gouts of slime. They also explode when you kill them, so don't get too close!

Finally, Spore Lords are created from creative and inventive souls, which somehow grants them not only the intellect to make decent tacticians in battle, but also hyper-mobile shapeshifters who can transform from solid flesh (well, "flesh") to a free-drifting cloud of fungus spores and then back again.