Many entries will link to other blog articles, which may occasionally break. If you notice a broken link and call it out in the comments, I will get to fixing it as soon as possible.
Anyway- this is the result of several years of writing and illustrating. The results are weighted towards mutations that are mostly neutral, that have positive AND negative effects, or just weird effects in general. This is how I tend to write mutations. The outliers are made to be less common and on the extreme ends of your roll. This table has been planned for quite a long time, so I am finally glad to see it finished! Total number of potential outcomes is pretty high. I think you'll get some mileage.
The form of life is mutable. Either through magic spell or mutagen, you are being changed. Whenever you fail a saving throw against a mutation, or are forced through one for whatever reason, you may roll on this table. If an entry does not specify a body part, or a mutation must occur on a certain body part, roll a 1d8 to determine what body part is selected. Certain races may have additional body parts- such as wings, tails, or long manes that may also be mutated or added. If a character is a centaur or has 4 arms, expand the table below to a d12 with the extra arms/legs.
Many entries on this table contain links to other pages. Click on the link and follow the instructions on that page to generate the result. Certain entries may also have small, nested tables in the form of lists. In these cases, roll the number indicated and then the result on the list is the number you use.
Bodypart Selection Table- 1d10
 Left Arm
 Right Arm
 Left Leg
 Right Leg
 You are permanently warped into a horrible genetic aberration, with a constantly shifting form. It is made up of many kingdoms of life; plant, animal, man. The creature has 1 less HD then your character's level, and becomes a mindless NPC monster. Bummer.
The monster then (1d3)- Goes on a rampage and attacks the nearest being, starts eating nearby corpses or greenery, or runs away to find a safe place to nest & brood.
 You are heavily degenerated. Reroll all of your stats, and take the results if they are lower then your current ones. You are simply scarred by genetic errors, poorly built structures, and a weakened and unhealthy body. Normal cure spells will not work on you, is this is what your body is meant to be like, as though born with this form. Only a wish or divine intervention can revert these changes. If you rolled none of your new stats lower then your older ones, then you instead degenerate into an ancestral, unevolved animal form. Orcs turn into pigs, Humans become featherless bipeds, etc.
 You have gained an innate weakness to one of the elements, present in your flesh or skin. (1d4) Fire, Cold, Lightning, or Acid has become your nemesis. You take double damage from this element. After you die, your corpse will reanimate as an undead weak to the same element you were in life.
 You grow a second “face” underneath your first. It's a bit like a goiter that grows under your chin and is smaller, but has eyes and a mouth. Roll a random set of Eyes and Mouth (teeth table) on the Cavern Beast Generator to determine its stats and what it looks like. The face is almost always asleep when you're on the surface, but its eye(s) blink open when you go deeper underground. The face also follows your mental commands, but has a bit of an animal mind that betrays your subconscious. The face will, for example, bite or spit at those you hate and are forced up close to, even if you wish to keep your dislike of them a secret, or lick the neck and face of a lover, even in public.
[5-7] You have become misshappen. Roll on the misshapen subtable on the Weird Monster Generator until you get an 8, then gain a special power rolled on that special power table. Add those limbs to your body, which are otherwise act as normal limbs. Extra heads have simplistic and similar, but still distinct personalities and voices, to you. Like an unoriginal conjoined twin.
[8-9] Roll on the Rat Mutation table. The next time you eat some cheese, roll on that table again.
[10-11] Your head morphs into an animal head. Roll on the Random Animal table to determine what animal it is. You will gain/lose a bite attack based on what head you get. Your stats do not change, but you may see better or worse, gain nightvision or antanee, have a powerful nose, etc. You can still speak your normal languages, but can also speak the language of that animal and partially communicate with members of that species. You also will probably no longer be able to wear a regular helmet, and your clearly inhuman appearance may give you an additional -1 to reaction checks with civilized folks.
[12-16] Roll on the Blood Mutations table.
 Your body's humors have been disrupted! One of your Four humors are underproducing, while the rest are overproducing. The humor you are having trouble creating is (1d4) Hot & Dry, Hot & Wet, Cold & Dry, or Cold & Wet. You now have to eat an entire meal dedicated to that humor, such as lathering it with spices or eating very specific foods. On the upside your body's overproducing of the other humors has increased your energy and activity levels. You can now be fully rested with just 4 hours of sleep, and heal +1 hit points per day as long as your humors are kept in balance.
[18-20] Roll on the Nose Mutations table.
 You grow an elephant trunk in place of your nose. The trunk can be used as a prehensile limb that can grip objects roughly, but can only use small weapons like daggers or clubs at a -2 to attack rolls. You can also breath through it, but you lose some of your sensitivity to smell.
The trunk looks (1d3) Like a typical gray elephant trunk, like your normal skin covering stretched into a weird trunk-like shape, brown and super fuzzy as a wooly mammoth trunk.
The trunk looks (1d3) Like a typical gray elephant trunk, like your normal skin covering stretched into a weird trunk-like shape, brown and super fuzzy as a wooly mammoth trunk.
[22-27] Roll on the Eye Mutations table.
 You gain Darkvision. This means your eyes glow in the dark- letting you see in darkness. Your eyes glow a specific color based on your race. Sneaking around without closing your eyes in darkness confers a -2 penalty to all Stealth rolls.
[29-33] Roll on the Hardcore Mutations table.
 Your mouth and digestive process changes. Your spit become mildly acidic, dealing 1 damage to creatures if not wiped off after an exploration turn and dealing minor damage to stonework or metals if spit on and left for long periods of time. This applies to all your bodily fluids, thus making you very dangerous to other people around you as well, though you are thankfully immune to it. Your stomach can use this spit, as well as its newfound ability, to digest basically anything. You can scrap lichen off the walls, eat any creature's meat, chew pinecones, etc. Basically anything biological, no matter how rotten or hard, can be eaten and its nutrients absorbed by you. You don't need to forage for food.
[35-37] Roll on the Teeth Mutations table.
[38-40] Crystals grow in your flesh. Roll on the Flesh Crystal Growths table.
 Crystals grow in your flesh. In this case, it is Azurite ore growing on your body on a random body part. Azurite is a blue ore with the power to transmit, store, and release energy. Roll on the Azurite Power Table to determine what type of power you gain by using Azuritre. These crystals also sap your body of its energy; take lose -1d6 Constitution from these leeching crystals. If this would kill you, you lose your energy over the course of a few weeks, granting a small chance to find a cure or removing the mutation before the Azurite turns you into a zombie, drained of all life force.
[42-46] Roll on the Leg & Feet Mutations table.
 Your legs fuse together to become something new. Your legs combine to become (1d4) the tail of a mermaid, the body or “foot” of a slug, the coiling muscular tail of a snake, OR the entire four legs and lower body of a random quadrupedal animal making you into something akin to a centaur. Roll 1d8 on the Random Animal Table to determine this animal in the event of the above result.
[48-52] Roll on the Miscellaneous Mutations table.
 Thy flesh twists. Roll 1d3 random Body Parts, which have twisted around backwards. Certain body parts, like the chest, do not twist backwards and are instead twisted into a spiral. Due to the severity of this effect, the next night you go to sleep you toss and turn- waking up in a very strange sleeping position and having 1d2 of your twisted body parts realigned to normal. You can have the permanently stuck body parts treated by physicians and healers over the course of several years to turn them back to normal. However, your joints in these affected body parts become much more flexible; if your head was screwed on backwards and then cured, you can turn your head around 180 degrees, if your arm was twisted backwards you can fully bend it back, etc. As a result, you gain Dexterity points permanently equal to the number of limbs twisted back.
[54-59] Roll on the Freaky Fingers table.
 Your arm warps. Roll a random arm, then roll on the random Arms Table on the Weird Monster Generator. This arm replaces the offending limb. It gains or loses its usefulness based on whatever arm you rolled, having similar stats and abilities. If you roll the human hand, it has tattoos and gains a streak of criminality (picking people's pockets, flipping the bird, goosing passersbys, etc.)
[61-62] Roll on the Hair Mutations table.
 Your limbs are undergoing a serious transformation. Blisters form, retracting 1d4 of your limbs into the huge bread-loaf sized pustules at the terminus of your joints. These pustules can be squeezed by you once per day to fire out tiny, milky white translucent tendrils that sting whatever they touch, with the effect of the sting being listed below. You lose the use of these limbs while they are “changing”, and lancing or destroying these pustules destroys the limb permanently. After one year, these limbs emerge as long gray tendrils that can be used as a rough prehensile limb that is safe to the touch for others, though lacking the dexterity of a normal hand or foot. The end of these tendril has a slit and can be opened to reveal a small tentacled “hand” or “foot” that has the fully effectiveness of the limb but carries with it your poisonous sting.
Additionally, all of these stinging tentacles you have have the effect of (1d2) save vs paralysis or be paralyzed for 1d4 rounds, or save vs poison else take 2d6 damage from the stingers.
[64-66] Roll on the Torso Mutations table.
 Roll a Random Bodypart. Then, roll on the skin coverings table from the Mutant Wasteland Guide Generator. This is the skin this bodypart is now covered by, losing its fur if you had any. You gain +1 AC if the area has natural armor on it from the Mutant table.
 Generate a Random Alien Organ. This organ grows inside your chest over the period of 1d4 days, and its purpose should be shifted to better fit a fantasy setting. You gain +2 hit points from the increased body mass and bulk, but (1d3) you must eat an extra ration per day, extraterrestrials from another dimension will stalk you to vivisect the organ and take it, or you must consume a rare and expensive spice mixed with water once a month for its specifics nutrients or else you will sicken and die over the course of 1d8 days.
 Regardless of your gender, you have become pregnant. Your body must carry the creature for 2d6+2 months, and then you will birth it through the most fitting opening. This creature is a 0 HD monster generated using the Cavern Beast Generator. It is helpless and feeble until it has at least 1 HD. It has imprinted on you and believes you as its mother, and will not ever attack you, but hates the sun and wishes very much to remain in the darkness. The creature gains 1 HD every 1d4 years it develops, growing its attacks and power the older it gets. It is considered fully adult when it reaches the HD it would have had if generated solely on the Cavern Beast Generator.
[70-72] You change race. Over the course of 1d6 days, you mutate into a totally different being, with some vague similarities between your old body type, voice, face, coloration and so forth with your new form. But you are still wholly different, gaining and losing racial traits or bonuses as normal. Roll on your favorite gonzo race table, or GLOG Race Table by Skerples.
 Roll a Random Bodypart. If that body part is holding a magic item, then it “fuses” with the item. Your skin starts to grow over it and meld it to your form. An item held in your hand has its flesh melded onto it, if you're wearing a magic necklace the necklace is covered by a layer of skin and dully glows through it, etc.The item is now stuck to you and awkwardly trapped within a layer of your skin, which can only be cut out with surgical tools. If there is no magic item touching that part of your body, instead this mutation hides in wait until a magic item is placed there or brushes against it. You cannot use this bodypart as normal or equip an item in that slot, but can make full use of the item that is trapped inside of you with its full modifiers and uses per day.
Additionally, over the years this item is consumed more wholly, breaking down and changing into a biological form. When a magic sword is fused subsumed by your arm's flesh, it looks the same as it did before, just melded to you. After many seasons, the sword will begin to have bone and keratin elements, mixing with your biology and eventually seeming as though it is wholly a part of your body. At this point the item can not be surgically removed, but it will regenerate if damaged and you gain more control over it. For example, items with a one use per day rule will now have two uses a day, but you must consume an extra ration to feed the energy cost and so on.
[74-75] Your brain experiences a surge of maturation and new structures form within it. You gain the abilities of a beginner Psychic. You may eventually learn a Psychic trick or even develop a full blown Psychic power through leveling up, and training with your new power. This power is not considered magical, and may even work in alternate realities where magic does not exist. However, by becoming a Psychic you have opened the door for astral beings, psionic creatures, and harrowing life experiences to all be able to both sense you as well as cause your mind harm from the psionic attacks or stress. Roll on the Psychic Trick table to see what power you can develop.
[76-77] You grow horns. The horns sprout from your head and can be used as a 1d3 improvised weapon in combat if you butt your head around. The horns appear as the horns of a (1d6) Bull, Mountain Goat, Demon, Antelope, Moose, Stag. In the case you rolled a Moose or Stag, they are not horns but actually antlers, and will fall off and grow back each year.
 Your skeletal structure painfully shifts and hardens. You gain a slightly different silhouette and a slightly different looking face, but otherwise look the same. You gain +1 AC from your newfound skeletal development, but lose -1d4 Dexterity. When you die, the skeleton inside your body is very strange. Roll on the Weird Skeleton Table.
 Your bodily constitution has changed considerably. Your body stores fat as a layer of thin, but tough blubber just under the skin. You gain +1d6 Constitution points and a considerable amount of heft, but are not much fatter then you were before. This layer of blubber has also made you resistant to cold damage. However, your overactive immune system means you have developed a new deadly allergy to (1d4) Wine, Paper, Glass, Honey. Save vs death on touch, no save if ingested.
 You begin to grow manfruits. Unless you're a woman, then it's womanfruits. Or “personfruits”, whatever works for you. These grow along your sides, hanging out from your body on small twigs that poke out from your flesh painlessly. These 'fruits' have no effect on you, and indeed taste and make you feel terrible if you eat them, but others can eat your fruits or sup their juices and restore 1d3 hit points and will also restore 1 point to any damaged attribute. You grow 1d4 fruits during Summer and Autumn, 2d6 fruits during Spring, and are bare for the Winter.
 You're half slime! Your skin and flesh sags and takes on a new viscosity, more like ooze or gel. Your bones remain intact, and are the only anchor points to your physical body- you're much like a skeleton jelly. Your body has a new consistency closer to that of (1d4) Wet Sand, Clay, Gelatin, or Liquid Cement. You take -2 damage from slashing or piercing weapons and you don't bleed.
Additionally; Your internal organs (1d3) have disappeared and your entire body volume does the job, now float freely around you and can be removed without harm for short periods of time, or have turned into spiders which seek to escape you from wounds and bite your foes whenever possible.
[82-83] Roll on the Rubber Forehead Alien Generator to determine what your face and forehead changes like- roll on the first two “Characteristic” tables. You also gain the benefit of their culture as a sort of newfound mental acuity in that subject. If your setting has more prejudice against mutated people, then this mutation is less egregious. If you've already rolled this one, instead just roll on the Characteristics table and then roll on the Terrible Knowledge table instead.
 Your body now naturally absorbs magical energy, much like a sponge. You suck up a specific type of energy; roll on the 6 Types of Magical Energy table. If you absorb enough of this energy, you start to glow its colors and can produce a minor magical effect relating to it by spending the energy. However, due to your body's newfound openness to magic, you suffer a -4 to all saving throws vs all spells.
[85-86] You grow a tail. If you already have a tail, you grow a second one. This new tail is determined by rolling on Priunt's Random Tail Table- from the Really Powerful Hirelings Table. You gain the tail and its abilities. If chopped off, you get a saving throw to have it grow back the next morning. The tail will always grow back the same type that you had before. If you fail this save, the loss of the tail is permanent.
 You gain a hint of the “Other” in you. You are not an Other, but the Others will ignore you, treating you as one of their own, or like a background noise as long as you do not attack them or interfere with their plans and cults. Roll on the Other Tell Table and you gain that tell. You also gain the ability to distinguish an Other by sight and smell.
[88-93] Roll on the Weird & Terrifying Powers table. Some of the powers are more mystical and abstract to work with mutations, in which case, just roll a d30 on the table, which is where the majority of the more physical and biological powers or mutations are.
[94-95] You develop a strange patch of skin somewhere on your body. Roll a random bodypart for the location. Roll on the Cavern Beast Generator skin table to determine what it is. You gain the benefit.
[96-97] Your pineal gland fully activates, and you grow your third eye on your forehead. You gain +1d3 Wisdom. Additionally, your eye has the special power of (1d4)- Seeing the Invisible, Seeing through all illusions, Detecting Magic, or Detecting Alignment.
 You experience an astonishing rate of growth and development, like a second puberty. Your oldest scars disappear, you grow an inch or two in height, and your secondary sex characteristics are enhanced. Restore any damaged attributes you have and roll 1d6 twice to determine two different random stats. These stats are improved by +1d4 points permanently.
[99-100] Roll on the Really Good Mutations table. Nice.