Magical Diseases for a Magical Setting, Part 1
Magical settings should have magical diseases. In a world with basilisks and ghouls, sicknesses with weird effects should be at least as common as those monsters are. To that end, I've come up with seven magical illnesses: three for this post, and four for the next. They have not been tested at the table, so use them all with adequate precaution.
The first paragraph describes each disease generically; I am imagining a high fantasy setting, but otherwise it is setting-agnostic. The mechanics are written, as usual, for 5th edition Dungeon & Dragons because that's what I use when I run high fantasy games, but I think the mechanics will communicate the idea behind each disease and allow you to adapt them to your system of choice. If I have any design notes, I'll add them as a footnote. Today I will tell you about the flickers, gilt pox, and princely ague. Next time I'll tell you about grave rash, kissing grippe, the weeping warps, and the wolfish fits.
Euricius Cordus, 1529, public domain (source)
The Flickers
The flickers are caused by a microscopic worm that often infects chickens, goats, and tortoises, but can make significant problems for humanoids who ingest them: the worms find humanoid hosts unsuitable and try to use their innate spatio-temporal magic to escape. Unfortunately, it takes a number of days before the host's body rejects the parasite's magic. Until then, the worm transports its host as well, making them "flicker" in space and time.1
When a creature that is not a beast eats food infected with the flickers parasite, it must succeed on a Constitution saving throw (DC 16) or contract the disease. Creatures that have advantage on saving throws made to avoid a magical effect have advantage on this saving throw. An infected creature can make this saving throw again whenever it finishes a long rest, recovering on a success; otherwise, the creature recovers by itself in 1d6+6 days. While a character suffers from the flickers, it gains a level of exhaustion every six hours; it can remove levels of exhaustion gained in this way by completing a short or a long rest. Outside of turn order, it takes twice as long as usual to complete any task (including travel), and any roll made to perform a task with time pressure is made with disadvantage. When in turn order, the creature rolls on the Flickers Displacement Table at the start of each turn and suffers the resulting effect until the start of its next turn.
Flickers Displacement Table
| d10 | Effect |
|---|---|
| 1-2 | Your speed is halved, you take a −2 penalty to AC and Dexterity saving throws, and you can't use reactions. On your turn, you can use either an action or a bonus action, not both. Regardless of your abilities or magic items, you can't make more than one melee or ranged attack during your turn. If you attempt to cast a spell with a casting time of 1 action, roll a d20. On an 11 or higher, the spell doesn't take effect until your next turn, and you must use your action on that turn to complete the spell. If you can't, the spell is wasted. |
| 3 | Your speed is doubled, you gain +2 to AC, you gain advantage on Dexterity saving throws, you gain an additional reaction, and you gain an additional action on your turn that can be used only to take the Attack (one weapon attack only), Dash, Disengage, Hide, or Use an Object actions. |
| 4-5 | You vanish, being thrown to a point in time in the near future. At the start of your next turn, you reappear where you were or in the closest unoccupied space. You don't remember this effect, but you can notice any obvious changes to your surroundings and deduce what happened. |
| 6-7 | You teleport to an empty space 5 feet away from you, chosen randomly. |
| 8-9 | You teleport to an empty space 10 feet away from you, chosen randomly. |
| 10 | Your timeline loops briefly back on itself, allowing you to co-exist with yourself for a moment. You teleport to an empty space of your choice within 10 feet of you and you leave a copy of yourself where you had been standing. The copy has all of the same statistics, traits, abilities, conditions, and items that you have and shares your hit points, spell slots, and other consumable resources (for example, if either you or your copy take damage, your shared hit point total is reduced by that amount). Your copy takes its turn immediately, before you take the rest of yours, and both you and your copy have a complete turn. If your copy ends any conditions on itself, those same conditions also end for you. At the start of your next turn, your copy disappears. |
Gilt Pox
Made by artificers centuries ago as a weapon in an ancient war, gilt pox is a disease with a dramatic and lethal progression: over the course of a month or more, it gradually turns its victims into solid gold, starting with the tips of their fingers and toes. In theory, gilt pox should be much rarer than it is, because it only transmits through direct blood-to-blood contact. However, a victim's solid-gold fingers and limbs can prove too tempting to the unscrupulous, who might try to chop off the valuable body parts. If those mutilators nick themselves in the process, they'll soon find they're turning to gold as well. Animals can catch gilt pox, too, so if an infected person is eaten by scavengers with bleeding gums, the disease spreads further still. Without proper containment, a single gilded stranger can turn a whole village into statues of gold.
If a beast, dragon, giant, humanoid, or monstrosity with an open wound (such as a creature that has half of its maximum hit points or fewer, or one that has recently cut itself as part of a spell or ability) comes into contact with the blood of an infected creature, it must make a Constitution saving throw (DC 18), contracting gilt pox if it fails. If a creature with one of the same creature types is hit by an infected creature's bite or claw attack, they come into contact with its blood and must also make the Constitution saving throw. If a creature with one of the same creature types uses a blade to cut parts off of an infected creature, it must make a Dexterity check, adding its proficiency bonus if it is proficient in the use of a relevant tool; on a failure, it cuts itself in the attempt and must succeed on the Constitution saving throw to avoid contracting the disease. A creature that receives a transfusion of infected blood immediately contracts the disease.
When a creature contracts the disease, it starts at stage 0. Every 24 hours after it becomes infected, the creature must make a Constitution saving throw (DC 18). A success on this saving throw has no effect. After three failures, the disease progresses to the next stage and the creature gains all of the traits described in that stage.
Stage 0: The creature has no symptoms. No effect.
Stage 1: The creature has faint tinges of gold on its extremities. No effect.
Stage 2: The creature's digits have mostly turned to gold. It has disadvantage on Dexterity (Sleight of Hand) checks and on all ability checks made to use tools or instruments, and it cannot add any portion of its proficiency bonus to these checks, even if it has traits or features that would otherwise allow it to do so. It has disadvantage on attacks made with ranged weapons.
Stage 3: The creature's hands and feet are mostly gold. It suffers all of the stage 2 effects and, in addition, it is unable to use ranged weapons. It also has disadvantage on attacks made with melee weapons and on Dexterity (Acrobatics) checks and Dexterity saving throws made to keep its footing.
Stage 4: The creature's hands and feet are solid gold, and parts of its arms and legs are turning gold as well. It suffers all of the stage 3 effects and, in addition, it can only use its hands for unarmed weapon attacks, or to hold a shield if another creature will bind the shield to its hand. It cannot cast spells with material or somatic components. Furthermore, its movement speed is reduced by 10 feet, its swimming speed and climbing speed are reduced by a further 5 feet, and it cannot add any portion of its proficiency bonus to Dexterity (Acrobatics) checks and Dexterity saving throws made to keep its footing. However, the creature gains +2 to AC.
Stage 5: The creature's limbs are mostly gold. It suffers all of the stage 4 effects, except that its movement speed is reduced to 5 feet, it can no longer climb or swim, and it cannot attempt to grapple another creature. It also has disadvantage on unarmed melee attacks made with its arms, and it cannot make unarmed melee attacks with its legs or feet.
Stage 6: The creature's arms and legs are entirely made of gold. It suffers all of the stage 5 effects and it is restrained. The creature loses the +2 bonus to AC gained in stage 4, but gains resistance to slashing and piercing damage made by non-magical weapons.
Stage 7: Gold is making inroads into the rest of the creature's body. It suffers all of the stage 6 effects.
Stage 8: Much of the creature's body has turned to gold, and it has difficulty speaking. It suffers all of the stage 7 effects. Furthermore, if it attempts to cast a spell that only has verbal components, it must first succeed on a Charisma (Performance) check or the spell fails. All other Charisma ability checks are made with disadvantage.
Stage 9: The creature is almost entirely turned to gold. It suffers all of the stage 8 effects. Furthermore, it cannot cast any spells.
Stage 10: The creature has fully turned to gold. It is petrified.
Gilt pox cannot be cured with a herbalism kit or by most magic. Any attempt to cure the creature of gilt pox by using lay on hands or a spell other than divine intervention or wish automatically fails and counts as one failed saving throw for the purposes of the disease's progression. An infected troll at stage 6 or lower can reset the disease to stage 0 by cutting off any parts of its body that have turned to gold, losing hit points equal to its stage number multiplied by its challenge rating; no other creature can reset the disease's progression by cutting off body parts in this way, regardless of whether or not they are capable of regeneration.
When a creature is cured of gilt pox, it retains the effects of whichever stage it was on. Once the creature is cured, greater restoration can remove all of the disease's effects.2
Developing a Cure for Gilt Pox
A researcher proficient in Arcana and Medicine can attempt to develop a cure for gilt pox. The researcher must be able to study at least three creatures infected by gilt pox over a period of two weeks; at least one of the infected creatures must be in stage 6 or later. The researcher can make an Intelligence (Investigation) check (DC 25) at the end of every eight hours spent studying the infected creatures and experimenting with treatments, expending 10 gp in materials for each roll. It gains a +1 bonus to the check for each creature beyond three that it can study, and another creature proficient in Arcana or Medicine may assist it in its research, granting the researcher advantage on these rolls. If at the end of fourteen days the researcher has accumulated ten successes, it has learned how to make a cure and has three doses of the cure on hand. If it has not yet accumulated ten successes and it still has access to three infected creatures which it can study, it may continue making Intelligence (Investigation) checks once per day, until it accumulates ten successes. Once it knows how to make the cure, it can spend two hours and 3 gp worth of supplies to make a Wisdom ability check (DC 12), adding its proficiency bonus if it is proficient in the use of a herbalism kit or alchemist's supplies; it produces a single dose of the cure on a success. If it attempts to teach another creature how to make the cure, the other creature can make a Wisdom (Medicine) check (DC 15), learning how to make the cure on a success.
Princely Ague
Some severe fevers can cause hallucinations, but a magical airborne virus called princely ague produces a very specific delusion in those it ails: they always believe they are monarchs. Of which kingdom they believe themselves to be the monarch varies from sufferer to sufferer. One might think she is the rightful queen of the land she's in, while another might believe he's a king in exile from a distant republic. Whatever the details of their fantasy, the delusion grips them so long as the fever (otherwise quite mild) persists. Its name is a joke about princes acting like they think they're already king.
If a humanoid, or a monstrosity capable of speaking a language, spends more than 1 minute within 10 feet of an infected creature, it must succeed on a Constitution saving throw (DC 8) or become infected with princely ague. It must repeat this saving throw for each infected creature within 10 feet and for every subsequent hour it spends in each infected creature's company. It automatically fails if it rolls a 1 on any of these saving throws. Once the creature becomes infected, it shows no symptoms until it finishes a short or a long rest. Upon completing a short or a long rest, the creature gains three symptoms, which it has so long as it remains infected with princely ague:
- it gains a level of exhaustion after every 3 hours of walking, riding, or light labour, after 30 seconds of heavy labour, and after 3 rounds of combat;
- it believes it is the rightful monarch of a kingdom of the player's choice, and cannot be dissuaded from this belief by any means short of curing the disease; and
- if another creature reinforces the delusion, the infected creature automatically fails Wisdom (Insight) checks to determine if the other creature is lying, believing what it says.
A creature infected with princely ague otherwise behaves normally and rationalizes any incongruities between their beliefs to the best of their ability. For example, it can notice that it has a fever, but cannot be made to acknowledge it has princely ague in particular. The creature's player can decide on the details of the delusion, but it must believe it is the only current rightful monarch of a kingdom the creature believes is real. The creature can make a Constitution saving throw (DC 10) every time it completes a long rest, and is cured of the disease after three successes (or two consecutive successes). A creature that has recovered from princely ague is immune to it for six months.
Of the magic diseases 5e provides, I most like cackling fever from the Dungeon Master's Guide and the gnawing plague from Van Richten's Guide to Ravenloft, called "the shrieks" and "the gnaws" respectively. I am of course adopting this naming convention for the flickers.↩
When writing gilt pox's mechanical expression, I had in mind my brother Nick's blog post about petrification. If you look at it, you might notice that I really cranked up some of the dials to make it a slow-acting but terrifying affliction. Because gilt pox takes so long to kill its victims, I think it's important to make it very difficult to cure; this should produce the right amount of tension.↩