Altered Alchemy

Witches, Alchemists, Hags, or other potion brewers usually can create this disease. Usually, one of these poisons food or drink with the disease. Sometimes the DM can make it into a potion, or make it given by a fungus, plant, or aberration of some kind. The target can make a DC 15 Con save, getting afflicted on a failure, or you can just make it unavoidable.

Effects

Stage 1: At first, nothing seems to be wrong. However, the afflicted soon begins to notice small changes. Only roll on the table once every day, and lower the effect and its duration (a age reduce only makes them a few months younger, a shrink might make them only shrink D4 inches). Every few days, the target must roll a con check. On a 5 or lower, the disease progresses to phase 2. On a 6 to 14, nothing happens. On a 15 or higher, the disease gains on success. On 3 successes, the disease fades away. Stage 2: Once stage 2 begins, the victim is seriously noting changes. They gain an effect every D12 hours, and the effect is only slightly weakened, the duration only slightly reduced. Every few days, the target must make a con check. Everything is the same as before, except it progresses to stage 3 and only returns to stage 1.
Stage 3: Stage 3 is when the fun begins. They gain an effect every D8 hours and the effect lasts fully, and its full duration. At this point, the disease no longer will fade, and can only be delayed. Every few days, the target must make a DC 10 con check. On a failure, the disease continues to stage 4. On a success, nothing happens.
Stage 4: At Stage 4, the target is rapidly changing, and the results don’t get pretty. Every D6 hours, they gain an effect, and must make a DC 10 con save or gain 2 effects. The effects are the same, but the duration increases by 50 percent (D4 hours to D6 hours). After D12 days + the targets con bonus, the disease continues to phase 5.
Stage 5: At Stage 5, the target is changing A LOT. The target gains 2 effects every D4 hours. The effects are increased slightly, and all durations are doubled. After D8 days, the target continues to stage 6.
Stage 6: At the final stage, the target can no longer hold it back. The target gain D4 effects every hour. The effects are increased a lot, and effects are permanent. At this point, the disease can’t really get worse, but the target must succeed on a DC 10 Con Save every month or transform into a aberration. As this, they gain an effect every D4 minutes, and lose their mind. Below are some extra stages (for fun), and the table.
Alternation Version: This is an alternate form of the disease, where the target doesn’t get worse. Instead, they gain an effect every D4 minutes, and the effects last D4 hours. The disease leaves after 100 minutes - con bonus.
Hyper version: This is an alternative form of the disease, where the target progresses much more rapidly. All hours are replaced with minutes. All days replaced with hours. Otherwise, the disease is exactly the same.

Table

d20 + d20	Effect	Duration
2	Become D12 Years Younger.	D8 days.
3	Become D12 Years Older.	D4 days.
4	One arm becomes small and crippled, - 10 to STR with that arm.	D6 days.
5	One leg vanishes, leaving you with halved speed, and loss of other benefits a leg gives you.	D4 days.
6	Grow D4 size levels.	D8 days.
7	Shrink D4 size levels.	D6 days.
8	Your Head becomes twice as large and heavy, making you unable to stand or keep your head up.	D6 days.
9	Your inner body becomes small, making your limbs and head unable to withstand themselves, making you quadrupedal.	D10 days.
10	Your insides become all jumbled, making you at disadvantage to all rolls, and causing other side effects (e.g. being unable to see, eat, move normally, or worse (leaking blood from openings, vomiting organs, etc))	D4 days.
11	Become inflated like a balloon, you weigh less than a pound (not including gear), and you have STR 1.	D4 days.
12	Become extremely obese, gaining 500 pounds and unable to wear armor, your movement speed halves.	D10 days.
13	Grow a tail, D4 feet long, and roll a D4. 1: The tail is fluffy, but otherwise useless. 2: The tail is sharp, and can attack as a bonus action for D4 piercing. 3: The tail is fast and leathery, and can attack as a bonus action for knocking prone. 4: The tail functions as a third arm.	D8 days.
14	Become a half-breed with a random creature, such as a dog, turtle, xorn, or other amusing change.	D6 days.
15	A smaller part of your body becomes three times as large, such as a nose, finger, or behind.	D10 days.
16	Transform into a different creature, keeping mental stats, but losing all others.	D8 days.
17	Become a vibrant color, such as neon blue or hot pink.	D6 days.
18	Gain D4 extra arms.	D10 days.
19	Gain D4 extra legs.	D4 days.
20	Gain a extra head. It conflicts with control over your body.	D4 days.
21	Transform into D4 copies controlled by one mind.	D10 days.
22	Become aquatic, gaining gills and fins, losing lungs. Swimming speed equal to double walk speed.	D10 days.
23	Grow wings, gain flying speed equal to your walking speed.	D8 days.
24	Become elemental, any type.	D8 days.
25	Switch races (use the reincarnate table) or use your own method.	D6 days.
26	Switch body form, such as becoming an ooze or becoming insectoid.	D4 days.
27	Become amorphous, gaining the ability to fit through holes of 1 inch or larger.	D4 days.
28	Gain a new feature (such as 4 eyes, a long beard, insect eyes, snake hair, etc)	D8 days.
29	Have your features swap (hair color, gender, hair length, height, eye color, etc)	D8 days.
30	Become a whole new creature, rolling on this table or another table D10 times to choose features, resetting all current features.	D8 days.
31	Have your body weirdly disfigure and melt, having limbs in weird places and a melted appearance.	D6 days.
32	Grow antlers/horns, can use a headbutt/charge headbutt attack for D6 damage, can't wear helmet.	D10 days.
33	Grow a coat of D4. 1: Scales. 2: Feathers. 3: Fur. 4: Thorns.	D6 days.
34	Grow a spider-like abdomen, gain the ability to cast web without material components, as an action, and climb in it. With increased effects, gain spider legs, and get shrunk 1 size.	D10 days.
35	D4 Limbs switch into other types of limbs, such as tentacles, claws, bird legs, fins, or wings.	D8 days.
36	Have your change, to become skeletal, stretchy, or the like.	D8 days.
37	Gain D12 tentacles.	D8 days.
38	Grow another less-important animal part, such as a snout, compound eyes, or whatever.	D8 days.
39	Start gaining effects much faster, hours turn to minutes for gaining effects. Effects end when this ends.	D8 days.
40	DM choice, or roll twice more.	D12 days.

Type

Magical

Origin

Divine

Cycle

Chronic, Acquired

Rarity

Extremely Rare