SCIENCE FUNGOIDS

Number Appearing: Small research groups: 2-8, population centers: 40-400
Size: 3-4 feet tall
Armor: Spongy exterior equivalent to leather
Resilience: As 3 human warriors, tenacious regeneration, extremely difficult to destroy permanently, resistant to magic
Intelligence: Human average but face intellectual challenges with inhuman determination unhampered by ethical considerations of any kind
Communication: Tiny voices like bursting bubbles, release clouds of interpreter spores that if inhaled allow permanent comprehension
Disposition: Charming, friendly, generous, overflow with manic joy, emit near-constant peals of high-pitched tittering
Violence: Generally left to humanoid bodyguards, otherwise by weapon
Enemies: Official policy of neutrality, big secret plans for everyone
Aims: Current overriding concern: learning everything there is to know about human(oid) physiology/psychology with a special emphasis on surface beings
Peculiarities:

• Formerly referred to themselves as Wise Gardening Fungoids, spent all energies on creating new and interesting fungal topiary until contact with the blind antler men and their space-born learning triggered a cultural revolution. Unlike the indifferent antler men, the Fungoids set themselves to mastery of the cosmos.
• Specialize in the development and propagation of a wide variety of medicinal, psychoactive, mutagenic, and frequently lethal fungal strains and eagerly test these innovations on human subjects willing to sign a waiver. Additional tests conducted on captive clone populations well out of public view.
• Often freely distribute weaponized puffballs (see below) and spore-laden caps that are known to produce currently unpredictable mutations to adventurers for further field testing if recipient agrees to record effects and return with data
• Underworld ecology now considered well-understood, interest has moved on to the surface world, specifically humanity, marked by the recent opening of the Fungoid Institute of Human Sciences, a magnificent facility on the shores of the Black Ooze River
• Unimpressed with Chaos godlings as a rule, but deal prudently with these beings and their minions 
• Boast the Underworld's only true air force (usable in chambers of sufficient size), composed of living dirigibles, gas bag organisms manipulated and permanently enslaved by allied sorcerers

Treasure: Generally carry enough ready cash in a wide variety of Underworld currencies to grease the wheels of diplomacy, sacks of experimental fungi as noted above

Sample Experimental Fungi  (for OD&D/Swords & Wizardry/that kind of thing):
The (exceedingly grim) anti-personnel puffball grenade
These roughly fist size fungal spheroids burst when met with any sufficient force (such as hitting the ground after a toss) and project a cloud of spores in a 10' radius. Human or human-like creatures exposed to this cloud must make a saving throw or roll 1d6. On a roll 1-4, consult the random result table below. On a roll of 5-6 the victim swells into a giant puffball and explodes the next round, throwing off a 20' cloud of spores. Any within this radius must roll for their lives as above.
Random result table
d4
1. Sudden fungal bloom from within body (perish with maximum unpleasantness in 2 rounds unless magically cured)
2. Funganthropy: victim's form copied (very imperfectly) and replaced by fungal tissue, transformation complete in 1 turn, insane rampage of random violence commences shortly thereafter, hit points doubled due to fungal resilience
3. Victim rooted to the spot by fungal tendrils from legs, fuse completely into immobile stalk in 1 turn, head broadens into cap shape, its all over
4. Puffball fungi begin to grow at alarming rate from every inch of victim's skin, dexterity compromised by -1d6, charisma rendered null and void. Can be carefully shaved off to relatively decent effect, but process must be performed at least thrice daily to mitigate otherwise appalling hideousness and clear and present danger to companions.