So a detail I needed was the 12 common most feared diseases in my setting.
Sadly disease fear mania sometimes gets people blaming minorities or foreigners or wizards or chaos or demons. The details and manuals of these plagues were written in ancient Exilon the first large human civilisation and little has been added since.
A standard effect of being infected is they are more easily exhausted (half activity your CON allows) and fail exhaustion related saves. Not resting may reduce your future saving throws by -2, fighting and working hard reduces saves by -4. A healer treating you can help recover and might grant you extra saving throws to recover if the success. Some herbs aby help your saving throws also +1 for a generic common one, higher plusses for specific uncommon herbs +2 or if very rare specific ones +4.
d12 Twelve Plagues of Exilon
1 Scarlet Plague - spread by contact with infected or personal belongings. Save on contact, success resists, failure results in a fever one hour later resulting in the victim red-skinned and as weak as a baby for 3d12 hours. At the end the victim must save, success is recovery but loss of 1 CON, failure is death. This can be caught again and again but you get +1 save vs it each infection
2 Black Plague - spread by infected sneezing or contact with infected buboes secretions. Save on contact if fail the next day develop -1 CHA and lose a d4 HP. Each make another save, success is recovery failure repeats CHA & HP loss. Repeat until survive or dead. Each point of CHA loss recovers a point per week but some scars remain and they are obvious. You can only get this plague once
3 Yellow Plague - spreads in bad water in hot seasons, especially wounds exposed to bad water of if water is drunk or an infected animal is eaten. Watr from streets or garbage or sewerage is often tainted. Save on contact resists a failed save within an hour of contact causes victim to have -2 on all rolls for a d6 days. The second save, success = recovery, failure = victim is -4 all rolls, cannot heal naturally or eat or hold fluids without diareah or vomiting for a d6 days losing a d6 each day. This can be caught again and again but you get +1 save vs it each infection
4 Blade Blight - wounds from blades or edges smeared in sewerage or other foul concoctions, if wound not treated by first aid save or lose a d3 HP an hour later if fail a saving throw. Sometimes Bullets or arrowheads or other injuries carry cloth fragments or other foreign material deep in a body that may require surgery or the victim takes a d3 damage a day. These effects are cumulative and may kill many wounded soldiers. Labourers injured in unclean workplaces may suffer this damage also. If a wound causes damage for a 3 days in a row the victim risks contracting a non-contagious version of the Scarlet plague each day also each day after the third
5 Green Plague - if sneezed on or touch secretions from infected, save success = resist, fail = lose a d3 damage and -2 all rolls success as victim chokes on phlegm, nose runs, throat is sore and bloodshot eyes leak puss like tears. Each day makes another save to recover or if fail repeat damage. Every seven days make an additional save or drown in your own phlegm. This can be caught again and again but you get +1 save vs it each infection
6 Bleeding Plague - infected by corpses of dead, blood and dungeon sewerage. Save to resist or lose d4HP per day as nose, ears, mouth, eyes and other orifices bleed. After a week save to recover or if the roll fails, body breaks into mass loose skin, bones and bodily fluid after a d4 hours of agony
7 Demon Toungue - people say it is spread by lies, witchcraft and demon worship but really it is from personal contact with a infected victims fluids. Save or infected on contact, if fail tongue swells and hurts and eating becomes painful for a d4 days, some have trouble breathing or communicating and makes gargling raspy sounds and cant move. After this period make a second save roll, success = recovery and and longer toungue, fail means the skull cracks open and the tongue crawls away to some dark lair it can infect victims with leaving a gory mess. Luckily rats and fish catch many of them before they infect wells and cisterns. This can be caught again and again but you get +1 save vs it each infection
8 Crotch Rot - a terrible venereal disease once exposed victim gets a save, if failed a week later genitalia starts turning into soap and dropping off the body. If not treated by healers within a month victim saves. Success is survival with horribly disfigured genitalia with urethra tubes visible if fail to die from infection with a horrible gaping wound and a bloated gas-filled abdomen. Some modern doctors inject mercury into the urethra to treat the ailment but this can be lethal also but many think is worth the risk. This can be caught again and again but you get +1 save vs it each infection
9 Dancing Plague - exposed by seeing others with the sickness dancing. Save resists for the day and risks repeated exposure. Failure makes the victim dance for 2d4 hours joining in with other victims. Once infected they must save each day to resist spending 2d4 yours dancing and a d4 damage. Mad dancers have -4 most actions but a skilled dancer ignores this penalty and can still fight and act. After dancing most pass out for 2d4 hours of sleep if fail a save. The dancers will gather and towns treat the infected mob with stages and band music. After a week the infected mob gather and dance their way to a location like a shrine d4 days away where the phenomenon ends. Some say there is a singing variant and a laughing disease. Some towns shun all dancing because of this illness
10 Lycanthropy - spread by victims of lycanthropes bites and claws, wolfsbane and belladonna treatments from herbalists or healers might provide some saving throw bonus. There are many strains but certain ones like wererat are very common. Some treatments used improperly poison the victim. The first year victims change into a monster each full moon (1-3 days) and don't usually remember what they do while becoming crueller and more predatory and haunted by dreams. After this, the victim knows and requires a saving throw or becomes mad giving into the beast and they will change whenever violence is called for. Those that try to keep their humanity often commit suicide if they cannot find a cure or feel they have committed terrible crimes. They may require saves to resist their bloodlust which makes it hard to be near people. When lycanthropy breaks out hunters gather to destroy them. A lone smart lycanthrope can live among humans or in wild for decades. The foolish insane ones are hunted and killed
11 Elfpox - a fast-acting highly infectious disease tends to run its course in hotspots for a week then burns out. The first save resists elfpox, the loser gets spots, a fever, headaches, no natural HP recovered daily, -4 all saves and attribute rolls for a d6 days. A second save determines if the fever ends in survival or a wizened hairless gnarled corpse in a foetal position. You can get elf pox again unless you have had goblin pox rendering you immune
12 Goblinpox - this takes time picking around goblin areas (like a dungeon or dead goblins). The first save if exposed is to resist. If fail the user loses a d4 CHA over a week as their skin develops horrible pox and the nose and ears enlarge and the skull grows pointy. After a month the infected get a second save. Success means recovery and failure means the victim has turned into a goblin or a hobgoblin depending on weight. A side effect of this disease is that if you have had it you are immune to elfpox. Sometimes a person with elfpox fever is taken to goblin town where goblins cover them in faeces and vomit and nest straw to cure the victim. Goblins were extinct in some lands but this disease brought them back. Many who recover retain some goblinish transformations still and feel a kinship to goblins many find humiliating
d12 Twelve Plagues of the Dungeon
1 Warp Fever - spread by chaotics and those exposed to warping emanations of chaos magic or mutagens or alchemical waste. The victim saves on exposure a success resists the effects but feel unpleasant for a d4 days -1 all rolls. Failure develops a minor mutation after d4 days. Surgery or banishment is the usual treatment and bigger kinder towns allow a mutant ghetto or shantytown to assemble. Too many exposures lead many to completely morph into non-human horrors. Some superior mutants seem to thrive and become increasingly inhuman
2 Purple Plague - caught by contact with sick and their secretions or tainted water. Save on contact or next morning awaken with purple swollen patches and lose a d3 hp. This is repeated each day as red blotches increase and leak puss all the time the victim is noisily flatulent for a d10 minutes per hour. If the victim dies the corpse bursts like a sack of dried scabby skin filled with purple puss and worms
3 Dungeon Lice - contact with dungeon garbage especially straw or sawdust from floors or monster bedding or clothing. Save on contact or start itching and -d4 on rolls, rerolling each day for severity. Each day victims must save or lose 1hp. The victim will not just get better. They require treatment including washing, boiling clothes, burning bedding and possessions all carrying vermin. A herbalist using plant treatments for itches and vermin end condition in a d4 days. A healer may use smoke, mercury or other strange treatments to remove vermin from a person or treasure with an hour of treatment. In icy weather, they are less infectious and mostly hibernate. Goblins and other monsters have their own folk treatments some worse than the problem. Lice eggs hibernate for years and awaken when animals breathe near them
4 Threadworms - clear vermicelli noodle like threads come from sewerage and corpses especially puddles in dungeons. They enter the body of a victim who fails a save and they lose 1HP per day. A fresh infection can be stopped by burning or cauterising the fresh wound for a d4 damage buy a healer or first aid skill. A healer, herbalist or apothecary or poisoner treatment can poison the worms and not damage the patient for 2d6 damage like a failed amateur or quack. Even if this poisoning fails the worms get a saving throw or dies, driving them from victims orifices and openings in a disgusting mess over a d4 hours
8 Mutango Fever - exposed to spores in dungeons or caves. Save or mushrooms sprout on body and turn into delicious mushrooms turn into fungus zombie over a week. As a fungus, it is immune to turning and holy damage but vulnerable to plant effects. The infected doomed victim feels euphoria and wants to eat more fungus and lets others eat its growths. After d4 months wandering with other zombies they collapse into a colony of edible fungus
11 Earworm - Mostly live in dungeon filth, blood and crypts. Worm eggs enters a victims brain if they fail a saving throw and begins to take over. After a week the worm provokes victim to violent conflict and become a cannibalistic berserker who only spares other worm hosts. Victims need a saving throw to avoid becoming berserk when angered. Poisoning or trepaning are the usual treatments but are risky. A skilled healer can lure the worm from the victim's skull with bacon and catch it. The victim leaves yellow fluid from the nose, mouth, ears and eyes at this stage