What Do We Know?
They were artificially created.
From the few survivors of the particular forest where the newest ones all seem to be turning up, there are tales of a lizard. Not a kobold... a full-sized alligator, who may have once been a druid and an adventurer, now turning to moss and mycelium among his children and subjects. They worship him as king and god alike. It is unknown whether he is still alive, or whether that matters at all when it comes to mushrooms, which grow heavily over his shape and around.
They CAN communicate... but we don't know how.
They can move or fight in coordinated groups or alone, respond to heard or mysterious orders from their god-king, even respond to some questions or comments in a spoken language... and it doesn't seem to matter which language. They make no sounds, and no signs. No psionic magic or telepathy technology has been found or intercepted. Our only theories are hive minds with spores or pheremones, and just enough sapience to comprehend body language and tone from spoken or signed word. And... they dance. Ritualistically, or just when idle.
They are remarkably easy to kill... and almost impossible to get rid of.
The mushrooms are soft, with no bones or cartiledge at all, held aloft only by the magic that gives them life. They can be dispatched with any weapon, or just a solid kick, and will break immediately into pieces or dust.
However, this only kills the bit that lives and walks and dances. Anything that has been touched by the corpse, or the dust from it, can and will grow additional, less sapient mushrooms within days, and more sapient mushrooms within weeks. The copies of the original will be smarter, and angrier, and several would-be mushroom dispatchers and enthusiasts have found themselves facing down a squad of fresh and hungry pygmies.
They will eat almost anything.
Standing on something, they can feed through tiny mycelium roots; and if left in the same spot may be significantly more difficult to move again. However, they can and will also eat through "mouths" that have no evidence of existing at any other time; which open wider and go deeper than should ever be possible. A well-fed mushroom pygmy will show almost no external signs of lumps or fullness, and the only visible evidence in the short term will be fragments and splatter from whatever was consumed so violently; and in the long term, a general lack of food-seeking until the large meal is properly digested.
Just about anything organic is at risk of consumption... including dirt, treated leather, wood, bones, hair and nails, scales and claws, un-processed grains, anything just about anyone else would consider food, and some more creature-sourced adhesives. The only known things they won't eat are rocks and metals.
They come in many forms.
Though the most common variant is a stunted and barely-recognizable humanoid form, the mushroom pygmies seem to also have morphs that function as mounts and companion animals. All of these, when sleeping in a way with limbs flat and eyes closed, can pass for a particularly large example of their component fungus.
Most mushroom pygmies will present and remain in a size between knee-high and waist-high on a human; at size or slightly smaller than goblins.
They're pretty cute.
As far as fancy pets go, there are definitely far more dangerous and problematic options. Mushroom Pygmies never get very large, are quite easy to feed, make no sound, are hardy enough to be kept outside in most climates, and can be bred without a companion (if you're brave enough to try and keep the spores contained). They don't live all that long, but are delicious when blanched and roasted or dried.
Additional Notes and Credits
The concept for this page was created in a collaboration project, based on a spore druid OC ("Eddie," an alligator-shaped Lizardfolk) who created and worked with mushroom pygmies rather than spore zombies for reasons of a slightly squeamish game master. A lot of creative license has been taken along the way.