There are a lot of fungi-analogs on Halcyon. Since most of the habitable area of the world is hot and moist with plenty of shade, this is a shock to exactly no one. Most of it is relatively benign. You may not be able to eat it and probably shouldn’t get too much on you, but almost none of it is actively gunning for you. Like fungus analogs everywhere else in the known universe, the vast majority of Halcyon pseudofungus is quite content to wait for you to die on your own before moving in to eat what’s left.
Anti-fungal measures are well-understood on Halcyon. Halcyonians know how to keep from getting serious fungal infestations. Wash properly with good soap (“good soap” on Halcyon would be right at home in a hospital in the greater Alliance), change your socks and let your shoes air out, and when it starts to burn between your toes break out the jungle foot cream. Every kid on Halcyon knows this stuff even before their teachers give them a thorough refresher in their health and physical education classes.
If an infection gets too bad, your local doctor can give you something that kills it in a few days. Even without the Patrol’s generational vaccines, fungus isn’t usually a major threat to a Halcyonian’s health. Of course, with so little of the land area explored, there are bound to be exceptions.
Out on an unexplored (or barely explored) island, there’s a whole different kind of fungus. This stuff is resistant to the antifungal drugs found in standard Halcyonian survival, first aid, and hygiene kits. It is also fast-acting and can kill someone over the course of several days if left untreated.
This Fungous looks like a mass of slimy white tendrils and mats of interwoven strands. It can be found on trees or other plants, and occasionally digesting some animal that fell victim to it.
Mention it in passing as part of your description of the jungle, but don’t otherwise say anything. If you want to give them some spooky foreshadowing, describe a creature it’s eating; bloated flesh like any other dead body, with visible Fungous on it and the ground nearby, and fungal slime oozing from any holes in the carcass. Make it as icky as possible so the players will have a suitably horrible image in their heads when one of their characters gets infected. Keep track of any surfaces it’s living on, though. This will be important if someone isn’t careful where they walk.
The Fungous infects its victims by skin contact or inhalation. Inhalation will happen to anyone coming anywhere near it. Just as on Earth, fungal spores are everywhere, and anyplace the Fungous inhabits will have plenty of its spores floating around. Fortunately, most people’s lungs are capable of keeping all but the thickest clouds of spores at bay; humans have been fighting off fungal spores since before they were even vertebrates. In game terms, require daily (or weekly) checks against Health at a significant bonus and only a critical failure will result in an infection of note.
If someone is hanging around a Fungous colony, increase the frequency of the rolls as you feel appropriate. Pausing to rest next to a tree with a significant patch on it may call for an additional roll, while venturing into a cave full of the stuff could warrant a roll every half hour at a much smaller bonus to resist.
Contact can be far worse. Human and Gliror skin is plenty thick enough to keep it out, and Thabbo hide might as well be armor. However, if the Fungous’s secretions find a break in the skin they can get inside very quickly.
In game terms, give anyone touching it a flat 10% chance of being potentially infected if they touch the stuff to represent a minor cut or scrape that was insignificant in game terms. If they touch it with something that’s got a wound that caused actual in-game damage, give them a 50-90% chance of potential infection depending on the wound. A minor wound like walking through the wrong briar patch should be at the low end, while a fresh gunshot or stab wound should be at the higher end, and if they slather it on a fresh amputation they’re getting infected. A potential infection can be resisted by a Health roll at a mild penalty. Let them survive a few encounters just to make them think it’s harmless and that you’re just trying to make them paranoid.
Inhalation infections result in a wet, hacking cough. The expectorations of this cough start out like any other, but turn white, slimy, and moldy-tasting within hours. If a player asks what it looks like, tell them it reminds them of the fungal slime they’ve been seeing around the jungle. If they don’t ask, wait a while then roll against their intelligence at a serious bonus and inform them they seem to be hacking up fungal slime.
From there the victim will develop a fever and the cough will get steadily worse until it leads to shortness of breath, periodic vomiting, and severe fatigue from both symptoms. They will also suffer quite a bit of muscle pain from all the clenching, as anyone who has had a nasty bout of the stomach flu will know all about.
As the infestation progresses, it will move into their brain to cause delirium and even more fatigue. Late-stage infection usually results in a dead-tired victim staggering and shuffling along in whatever direction their friends point them until they sit down to rest “for just a minute” and can’t get back up. This delirium is perfectly mundane. They are not turning into a zombie or anything similar.
If left untreated, they will eventually drown in the Fungous filling their lungs. Give them several days at least. If you feel like rolling for it, require repeated health rolls to keep from getting worse, with failures resulting in loss of their health stat. A critical success should restore one point of lost health or cure them if they have full health.
Contact infections act like pretty much any other infection. Redness, swelling, pain, and fever. After a day or so, start making health rolls. A failure results in damage to the affected area and a critical failure causes it to spread to an adjacent area. If a limb is crippled by the Fungous, treat it as a permanent crippling injury, but keep rolling for damage; once it reaches the threshold for limb loss, it rots off completely. As the Fungous takes over, it will slowly eat away at the victim’s tissues, and once it reaches the crippled stage it will start leaking fungal slime. The process can be arrested with amputation and cauterization, but even then there’s a chance it has spread far enough in their blood to keep right on growing.
After death, the victim will be consumed by the Fungous. Treat it like the standard bloating and decomposition process, but much faster and accompanied by Fungous leaking from every hole it can find. This includes natural orifices, wounds, and new holes made by the Fungous either eating their skin or torn by bloating. The entire area will have much thicker spore density than other areas; the body is a Fungous colony at this point. Needless to say, a Fungous victim is an extreme health hazard to anyone nearby.
An infected victim has two real options: hope they survive the trip to a hospital or die and have their body burned so it doesn’t spread.
If one of your PCs decides the best way to deal with an infected character is to skip right past the “they died from the infection” part and go right to “set them on fire,” you should have a pretty good idea who to infect next. Tell them when their victim died, his screams blew concentrated spores in the flamethrower fanatic’s face. And unless he’s been wearing a spacesuit since before he got to the island, he will have been exposed.
Once a victim is brought to a proper hospital, a cure can and will be found quickly. As noted above, Halcyonians know how to deal with fungus. It’s just that this fungus is a weird one that will take some study. The catch isn’t finding a cure, it’s getting the victim to people with the skills and equipment necessary to cure it.
Scenario Tips
While the Fungous will quickly become the primary “antagonist” of an adventure, it shouldn’t be the opening act. Instead, put the PCs on the island for any other reason you can think of. Ideally have it appear after several sessions on the island. This not only helps blindside them, but provides some plausibility for why nobody else seems to have been infected yet; players are notorious for wanting to know just how their big macho heroes just came down with a disease even the scrawny little nerd back at the base camp has avoided completely.
Keep in mind everyone on the island has been exposed to the Fungous. The people back at base camp who never ventured into the interior have the least exposure, while the exploration teams will have the most. Unless a character arrived on the island in a spacesuit or similar sealed suit and has never taken it off, they will have been exposed. Even if they never took it off but ate something from outside the suit (they have), they will have been exposed.
Don’t let the PCs do that. They have no single in-character good reason to do so, and it’s boring. If anyone shows up fully suited, it will be a containment team that comes in to clean up the mess the PCs made.
When introducing the Fungous, think Predator. The protagonists weren’t looking for an alien trophy hunter, they were (supposed to be) rescuing hostages. Have them doing something else completely and then have someone start coughing or notice their arm turning red and starting to hurt.
The drama will come from two main sources: getting the infected character(s) to a form of transportation suitable for getting them to a hospital, and worrying about the people back at base camp. A Fungous infection scenario is a race, not a firefight.
Again like Predator, you can very easily end the scenario with the surviving PCs getting to the helicopter off the island and telling them they’re being taken to a hospital (or hospital ship) for treatment. Let them sweat until the next session (tell the player “your character is still undergoing treatment” if they ask before the next session) and let them know how it turned out only after everyone shows up for the next game.