Starting on planar myconids now...
Physarid
by Cab Davidson
| Stat | Physarid |
| Armour Class: | 2 |
| Hit Dice: | 1** to 20** |
| Move: | 15' (5') |
| Attacks: | 1 per HD |
| Damage: | See below |
| Number Appearing: | Special |
| Save As: | F1 to F20 |
| Morale: | 8 (12) |
| Treasure Type: | Zero (M) |
| Intelligence: | 20 |
| Alignment: | Lawful |
| XP Value: | 12 to 4175 |
Whether the physarid is truly a myconid is a matter for moral and natural philosophers to judge. Some speculate that it and its ilk are closer to the slime molds, such as green slime, which in appearance it is very similar to but with a bright yellow colour. It is from 2’ to 40’ across (2’ per HD) when at rest, and around ¼” thick (with a volume from around a quarter of a cubic foot to around 105 cubic feet). They can form almost any shape they choose using that volume, including that of other creatures, albeit only becoming facsimiles made up of yellow slime.
It is unclear whether each individual physarid myconid is part of a greater overall myconoid, or whether indeed each is a separate intellect at all. All physarids seem capable of splitting into individual myconids, down to 1hd in size, and of rejoining with any other physarid. They grow by consuming all kinds of organic matter, which individual myconids gather, and once they get above 20HD in size they lose the capacity to move and must either merge with the ground or bud out new myconids. And when a myconid from one physarid myconoid encounters myconids or myconoids of another, they can can merge with that individual instead of their parent. Thus where physarids are found, they can be viewed as an entire dispersed organism of immense intellect.
Physarids never choose to attack intelligent prey, viewing the consumption thereof an uncivilised and immoral act. But theirs is also a lifestyle of abhorring waste, and when attacked they will defend themselves and consume an aggressor. They may pick up and use any weapon if in humanoid shape, and have the curious capacity to gain weapon mastery therewith as the use it, essentially gaining one level of mastery per three rounds that they have handled a new weapon. But this is rare, they prefer to use their natural attack which is identical to that of green slime. They can produce up to 1 pseudopod per HD, and each can attack a foe up to 10’ away. A strike dissolves cloth or leather instantly, wood and metal in 6 rounds, but cannot dissolve stone. Physarids may clings to surprise a foe. Once in contact with flesh, it sticks and turns the flesh into physarid. It cannot be scraped off, but may be burnt off, or treated with a cure disease spell. A pseudopod may be burned off by inflicting 10 points of fire damage to it. If the pseudopod is not burned off, the victim will turn completely into green slime 1d4 rounds after the first 6-round (one minute) period. Burning does half damage to the green slime and half damage to the victim. While a physarid may attack a victim with multiple pseudopods, it is rare that they choose to do so, preferring to warn a victim with a single attack to begin with. If killing their foe becomes necessary then they are quite remorseless and will pursue a persistent foe to the ends of the earth if necessary.
If defending their greater myconoid, individual myconids will fight to the death (morale 12), but they are otherwise quite rational in any decisions to fight or retreat (morale 8).
The number of physarids encountered is variable, depending on how close their myconid is and what task they are trying to accomplish. There will usually be 10-15HD of physarid working on any task, but their disposition (15 1HD myconids, 1 15HD myconid or anything inbetween) is variable based upon what they are trying to accomplish. Any combination of physarid HD can be created from their total mass, if in continuous contact, in a single round.
Physarids are native to various outer planes with a Thought bias, and to the elemental plane of Air. They are seldom found on the Prime plane, and can thrive there should the need arise. They feed on all manner of organic matter, preferring decaying plants but at a push can digest nearly anything. Their immense intellect and near limitless lifespan means that friendly relations with them are of great value to those seeking knowledge, and is wise not to tangle with them, for their memory is long and their patience in seeking restitution legendary.
The science bit - Physarum polycephalum is one of my favourite living things. Slime molds are always a delight to find when out foraging or just wandering through the woods, and I tend towards thinking that beasts like green slime are best thought of thus. Here's my fantasy take on an intelligent planar slime mold because, heck, why not?