Below is my contribution to a "contest" over on the OSR Discord. I cooked this up in a few hours and don't typically homebrew for the GLOG, but I'm fairly happy with what came out of it. Hope you enjoy, and while you're at it, check out the blogs of the other participants as well:
Micah
Ambnz
Lexi
Type1Ninja
Isaak Hill
wr3cking8a11
Oblidisideryptch
rtx
MycorrhizanMicah
Ambnz
Lexi
Type1Ninja
Isaak Hill
wr3cking8a11
Oblidisideryptch
rtx
A: Parasitic Passenger, Photosanisus
B: Distributed Dexterity
C: Genetic Graft, Emergency Spores
D: Grass Menagerie, Forced Fruiting
Okay, yes, all plants have mycorrhizae. But not like you, the mycorrhizan. You’re special. You can think and reason and speak (well, in a sense). When a mycorrhizan colonizes a plant, it uplifts it, turning it into a mobile being with the mycorrhizan acting as its brain. Unlike animals, plants don’t have much force of will (usually) so the mycorrhizan doesn’t have to worry much about the plant changing the way it thinks, beyond perhaps imparting some instinctual thoughts (why do you like meat all the sudden? Oh, right, pitcher plant). The mycorrhizan is also a habitual drifter, changing bodies as one might change haircuts or favorite lunch spots. Luckily for the plants, they just continue life as they normally would have, assuming the mycorrhizan didn’t leave them high and dry, away from life-giving soil.
Parasitic Passenger
The mycorrhizan does not have a body of its own. Instead it survives and moves by parasitizing plants. It requires 10 minutes for the mycorrhizan to spore and colonize a new plant, and a further 10 minutes to adapt the new plant’s anatomy into something mobile. The mycorrhizan can be uprooted safely by outside force during the latter stage. It can change its host plant once per day. The previous host is unharmed and will return to being a normal plant. However, it will be quite sad.
There is no restriction on what plant the mycorrhizan can colonize, however newly colonized plants possess only level+1 HP to start, as the mycorrhizan takes some time to integrate into the new host. When taking on a new host, the mycorrhizan’s STR, CON, and DEX are changed to reflect that of the host, at the GM’s discretion.
Plants parasitized by the mycorrhizan do not grow as normal. Instead the mycorrhizan can bend and twist their branches and roots into crude semblances of animal limbs. By default, the mycorrhizan can only control six limbs at once, and only two are capable of fine manipulation akin to human hands. If the mycorrhizan remains rooted for an extended period of time, it may make the host plant grow at an abnormally fast rate in exchange for losing the ability to control its movement. The mycorrhizan also has the ability to twist the host into any other reasonable structures with its branches and roots
Photosanius
The mycorrhizan is a plant. Well, more technically the mycorrhizan is a sentient fungal colony that lives on a plant’s roots and allows it to synthesize nutrients and minerals, but for our purposes, it’s a plant. As a plant, the mycorrhizan will naturally heal rather quickly over time given adequate food, water, and sunlight. As long as the mycorrhizan has access to fertile soil, water, and sunlight within a 24 hour period, it will regain 1 HP/hour while rooted. In the absence of any of these three, the mycorrhizan is unable to regain HP. Torches do not count as sunlight. Some magical light probably does. The mycorrhizan suffers from starvation and dehydration at the same rate as a normal human unless its host is specifically resistant to either.
Distributed Dexterity
The mycorrhizan has developed the ability to control more of the host at once. The mycorrhizan can now control ten total limbs, four of which possess the dexterity of human hands.
Emergency Spores
Upon reduction to 0 HP, if the host’s roots are still intact, the mycorrhizan can immediately release a cloud of emergency spores instead of dying along with the host. These spores may colonize any nearby plant. The new host is at 1 HP due to the hurried nature of spore release and cannot move or regain HP for 24 hours due to the tremendous amount of energy required for the mycorrhizan to establish a viable colony.
Genetic Graft
The mycorrhizan has mastered the ability to both integrate the genetics of other plants as well as maximize those of the host plant. If rooted for a full day, the mycorrhizan may perform one of two options.
A. The mycorrhizan devotes energy towards magnifying the expression of features of the host. Thorns may be grown into offensive weapons, poisons secreted in deadly amounts, sap production increased to provide food for others, thick bark grown in defense. GMs should allow any feasible exaggeration of a defining feature of the plant and provide a reasonable narrative or mechanical benefit.
B. the mycorrhizan integrates a sprig from another plant into the current host, adding beneficial characteristics from the donor sprig to the host in a manner akin to A.
The mycorrhizan can only perform these actions a combined total of [level] times on a given host.
Grass Menagerie
The mycorrhizan can now maintain multiple hosts simultaneously. INT/2 plants can be colonized by the mycorrhizan. The mycorrhizan cannot, however, distribute its consciousness and can only actively control one host at a time. It takes one round for the mycorrhizan to change active hosts. The others act as normal plants but will maintain whatever physical position and configuration the mycorrhizan left them in.
If at any time the mycorrhizan controls more than INT/2 hosts, whether due to a loss in INT or simply moving over the cap, one of the hosts, excluding that which currently possesses the mycorrhizan’s consciousness, spontaneously manifests a consciousness. Congratulations, is a boy/girl/mycorrhizan! The new being is likely to wander off if it’s not in imminent danger, but is otherwise a normal, sapient creature.
Forced Fruiting
By expending half of its maximum HP, once per day the mycorrhizan can cause the host to produce a bountiful harvest within minutes. Double the amount of produce typically expected from a single host plant. The produce is particularly nutritious and restores 1d6+level HP. The mycorrhizan obviously cannot eat its own produce. That would be silly.