One of the bad and good parts of Dungeons & Dragons 5th Edition is the uniqueness of diseases. Poisons occupy a weird place where it is a damage type, a condition, and then also competes against acid as a damage type. Poisons used in combat are unique things, and the Dungeon Master’s Guide has a list of really cool ones, not to mention some more I homebrewed to fill the power differential. Diseases, on the other hand, are really just discrete rules. Each one is different, requires its own sidebar, and is really only similar in the way defenses interact with them. That is, immunity to disease provides immunity to any specific diseases, advantage against disease provides advantage when you make saving throws against the disease, and so on.
There are few cases provided in the Monster Manual. The aboleth passes an unnamed disease to you, should you be hit with its tentacles. This disease turns you into a stinky fish person. It really gives you that Innsmouth look. Lycanthropes pass on a curse, rather than disease. Ghouls and ghasts have a paralyzing touch that isn’t a disease. Mummies curse rather than cause disease. You get the picture. The DMG provides cackle fever, sewer plague, and sight rot as examples, however. The 5th-level necromancy spell contagion lists six possible examples: blinding sickness, filth fever, flesh rot, mindfire, seizure, and (my personal favorite) slimy doom. Oh, and harm is a disease…for reasons. It’s really all over the place, is what I am saying. Which is good and bad. It’s not constrained, allowing a really wide variety of things to be possible. However, it doesn’t provide all that much in way of direction and consistency.
How different are they? Well, let’s take a look at the ones in the DMG. Cackle fever has a gestation time of 1d4 hours from contraction. You become feverish and disoriented, manifesting as a level of exhaustion. Any time you are stressed, you have to make a middling Constitution saving throw (DC 13) or suffer 1d10 psychic damage and become incapacitated with laughter for 1 minute. The laughter is the method of transmission, so if people are within 10 feet of a laughing subject, they have to pass a low Constitution saving throw (DC 10) or contract it. If you succeed, you have immunity for 24 hours. During long rests you can attempt to recover. If you make your saving throw, you lower the DC of further saving throws you have to make by 1d6. When the DC reaches 0, you are cured. If you fail three times, you gain a random, indefinite madness.
Sewer plague is a generic term for plagues and illnesses that crop up from places being groady to the max. The initial contraction is fairly low (DC 11) , though the vector could be touching something gross, being bitten by a rat, eating rotten food, and so on. Instead of contracting the disease in hours, you manifest symptoms in 1d4 days. From that point, you basically have the flu. Your symptoms give you levels of exhaustion, at the same point of difficulty. If you fail a save during a long rest, you gain a level of exhaustion. If you pass a save, you lose a level of exhaustion. If you reach a point without exhaustion, you are cured. Otherwise, you can die. Pretty straight forward.
Sight rot does what it says on the tin. You get bleeding eyes and you go blind. The vector is infected water, and staving off infection is pretty hard (DC 15). You start showing signs the next day, first getting a flat -1 penalty to anything sight related, and grows worse over long rests. If you reach -5, you are blind and need specific spells (lesser restoration or heal) to cure you. It can also be cured by a specific flower to go quest after.
As you can see, these are all wildly different, with sight rot even coming with built in quest mechanics for adventure. I fully support things like this where the answer isn’t “throw a cleric” at it. Yes, I know it might sometimes by a druid or paladin instead, you know what I mean. This diversity is great for gameplay, but tough on framework. Unfortunately, looking at the aboleth disease doesn’t do much to clarify this.
The aboleth disease is difficult to stave off (DC 14 Constitution, the aboleth is a challenge 10 creature) and is fast acting (it’s a combat disease). For 1 minute, nothing happens and it can be cured by things that cure disease easily. After 1 minute, only heal works and the creature is now a fish person, needing contact with water to live. Not all that much in common with the others.
If you are trying to draw some throughlines, you can sum up some general rules from these examples:
- Target Constitution for saving throws
- There is a permanent state for all diseases with enough failure
- Damage is reserved for combat diseases
- Disease progression can include cure methodology changes
These are incredibly general, and point three can be up for debate (this is based on a small sample size), but these are some good guidelines to keep in mind as you create disease. The DCs are important to keep in mind, too. DC 15 is very meaningful, while DC 10/11 is still not insignificant. It seems really low, but bounded accuracy is really doing its job in this edition, provided you aren’t going nutso with the magic items.
I definitely think diseases should make appearances where possible. There are curatives, preventatives, and immunities that classes possess, and getting to take action or show off is cool. So, with all this in mind, let’s come up with a couple more diseases for general use.
Arcane Cough: This disease targets scholars poring over ancient tomes. While suffering from the disease, performing spells with verbal components are increasingly difficult. Symptoms manifest 1d4 days after infection, and include joint paint and persistent coughing.
Whenever the infected creature attempts to cast a spell with a verbal component, the infected creature must make a DC 11 Constitution saving throw and become incapacitated with wracking coughing for 1 minute. The spell slot is not expended if the creature fails the saving throw. The creature can repeat the saving throw at the end of each of its turns, ending the coughing and the incapacitated condition on a success.
Any humanoid that starts its turn within 10 feet of an infected creature in the throes of wracking coughs must succeed on a DC 11 Constitution saving throw or also become infected with the disease. Once a creature succeeds on this save, it is immune to the wracking coughs of that particular infected creature for 24 hours.
At the end of each long rest, an infected creature can make a DC 11 Constitution saving throw. On a successful save, the DC for this save and for the save to avoid an attack of wracking coughs drops by 1d4. When the saving throw DC drops to 0, the creature recovers from the disease. A creature that fails three of these saving throws gains a level of exhaustion that can only be cured with a casting of greater restoration or more powerful magic.
Notes: This is an exploration hazard disease. Characters exploring ancient ruins or lost libraries or dangerous tombs might have to contend with this disease. It would predominantly be carried by scrolls and spell books, serving as a danger to scholars and magic-users. It slowly accumulates permanent exhaustion, and takes hold at the worst of times, when a magic-user is attempting to use magical words. This is a real problem for many characters, but it is also on the milder side of the diseases. The DC 11 is problematic at lower, and even into low-middle levels, but eventually becomes something of a non-issue.
Swarm Rot: (carried by demonic claws or bite) If the target is a creature, it must succeed on a DC 12 Constitution saving throw or become diseased. The disease has no effect for 1 minute and can be removed by any magic that cures disease. After 1 minute, a swarm of black flies erupts from the wound, all healing provided to the creature is re-rolled, with the lowest result of each die taken, and the disease can be removed if the creature is currently benefiting from Protection from Evil and Good when the disease is attempting to be cured. When the creature is at or below half of its maximum hit points, it takes 5 (1d10) necrotic damage 10 ten minutes unless it is attended to with a charge from a healing kit before 10 minutes have passed.
Notes: This disease would be a combat disease, transmitted by demons or other monsters with unclean claws. Since demons are a huge challenge range, we can target something around challenge 5 or 6. From there, you could scale the DC up or down pretty easily. It’s a pretty gross disease, and the image is pretty clear: flies or maggots are munching on your bleeding flesh, making things worse for you. If you aren’t cured, you have a swarm of flies forever until you eventually die from the necrotic damage. Protection from Evil and Good is there to carry through the idea of demonic possession being part of this disease. To fully clean it, you have to sever the link of the flies.