d100 Subterranean Mutations

So veins touches on this topic a bit but I had envisaged stuff like this before to turn creatures and humanoids into subterranean versions.

Some great stuff here for Veins on where do underworld folk get food, including gating to poor Xor and eating it....crossover!
https://falsemachine.blogspot.com.au/2017/09/feeding-cities-in-veins-of-earth.html?showComment=1505513309366#c8169268424875447205

As some mutations here explain many creatures in underland have adaptions to reduce needs for air and food and water. No luck for visitors though. Squeezing is mentioned too as a adaption to moving in confined spaces. A well evolved underdweller will become worm like and can burrow through earth able to breathe.

Mutations so Far
Xor Bio Mutations
Necro Mutations
Reptilian Mutations
Diabolic Mutations
Plant Mutations
Faerie Mutations
Mental Mutations
Third Stage Mutations
Law Mutations (to be revised under current mutation style)

errata at bottom of this post also as first two never got taint source tables

d12 Sources of mental mutation

1 Subterranean ancestor tainted bloodline
2 Exposed to strange radiations from illuminated caverns
3 Contaminated by fungi spores
4 Contaminated by strange food of the deep
5 Strange parasites entered body triggering change
6 Exposed to disease from the deep
6 Supernatural radiance of strange crystals

7 Poisoned by trans uranic elements and strange metals

8 Curse of the deep gods on you for transpression

9 Malnutrition and light deprivation triggers strange change

10 Venom of some creature triggered changes

11 Ancestors spent a era as cave dwellers

12 Dark elves want to help you survive in the deep and use dark pixie dust on you

d10 basic types
1 Facial/sensory
2 Skin
3 Torso/body
4 Abdomen
5 Arms/manipulation
6 Legs/locomotion
7 Mouth
8 Cranium/skull
9 Organs
10 Brain

Minor cosmetic mutations may have slight gamble effects not mentioned up to GM
Major mutations effects definitely gamble

d100 Minor Cosmetic Mutations

01 Eyes go white and become light sensetive

02 Ears become elongated and bat like become very accute to food in dark
03 Nose enlarges and split like a bat or star nosed mole becoming very acute
04 Eyes become catlike and highly reflective providing low light vision
05 Develop whiskers like a rat or cat for sensing possible crawl spaces
06 Eyes become insectoid and compond 360 degree vision
07 Eyes covered in transparent layer of skin giving a blank featureless face
08 A glowing lure grows from forehead providing some light
09 Antennae grow from head highly sensitive to movement
10 Eyes glow providing some light
11 Skin becomes pallid like albino requires no sunlight
12 Skin becomes grey or dull light blue
13 Flesh develops stony colour and texture blending into some geologic types
14 Flesh becomes puffy and wormlike, body more flexible,  streamlined for squeezing
15 Loses all body hair, covered in wrinkly loose skin
16 Flesh becomes tight and skeletal looking, easier to squeeze
17 Skin becomes jet black and shiny with symbiotic fungus 10% less food
18 Covered in soft fine mole like hair, streamlined for squeezing
19 Covered in reptilian scales +1AC
20 Skin becomes slimy like amphibian and mutant prefers humidity
21 Low body temperature and metabolism 25% less food
22 Less air required 25% less air needed, less harm from bad air
23 Hold breath extra ten minutes if prepared
24 Ably to perform hard labour like dig or swim or run twice as long
25 Increased life span by 25% due to metabolic stability
26 Able to hibernate once a year for up to 3 months if well fed with fat stores
27 Improved fluid retention 25% less water required
28 Double jointed and highly flexible for squeezing or escaping
29 Shrink 25% to consume less resources and squeeze more easily
30 Improved temperature regulation to resist hypothermia
31 Can subsist from chewing roots and fungus and things growing under the earth
32 Can subsist from eating worms, bugs, grubs and creatures of the earth
33 Can sense opposite sex and how viable for reproduction they are from pheromones 
34 Obtain required water entirely from food
35 Offspring double gestation period and lowered fertility
36 Suppress reproduction of weaker adults of same gender in proximity after a month
37 Remain fertile into old age
38 Can feed offspring by shedding skin for them to eat
39 Female produces egg or eggs after gestation
40 Can subsist from rotting feces and organic matter
41 hand claws suited for digging or d3 damage 
42 Arms are flush and shoulders are reduced, body structured for squeezing
43 Arms atrophied and smaller her help squeeze o burrow through ground
44 Suckers or claws on hands adapted for climbing and clinging to surfaces
45 Small set of mostly useless vestigial arms growing under normal arms
46 Less fingers hands more like mittens or crab claws
47 Rubbery elongated fingers good for fine manipulation and climbing
48 Elongated arms for climbing or snatching prey reach feet standing
49 Sticky secretions on hands improve grip
50 Arms are flattened with large flat hands for burrowing and swiming
51 Short stunted legs with flat feet for shoveling dirt
52 Clawed large shovel like feet for digging and swimming through soil
53 Hook claws on feet designed for climbing and hanging upside down even while asleep
54 Legs long and thin allow to squat close to ground or reach high
55 Foot claw can inflict d4 if rake victim if close or while wrestling
56 Feet can sense through ground sounds like digging or unsound walkways 
57 Feet can taste ground for traces of organic matter in soil or on ground
58 Feet have hooks or hooked claws can hang from
59 Extra set of smaller skinny legs for stability
60 Feet become smaller nobbly hard hooves good for climbing
61 Mass of tentacles surrounding mouth with beak
62 Insect like tube for sucking fluids and food
63 Tube like snout with long tongue excellent for eating ants and termites and worms
64 Complex mouthparts like insect or spider that can hold food and chew
65 Lamprey like feeding tube extends from mouth to feed
66 Can swollow surprisingly large live animals with a single gulp like large rats
67 Rows of shatp teeth fill mouth go down throat, d3 bite
68 Throw up digestive fluid onto food then suck up mess with toothless mouth
69 Mouth seems invisible blank space when closed
70 Froglike mouth and tongue  
71 Elongated domed skull almost fetal
72 Semi transparent skin and skull exposing brain and bones
73 Huge apish jaw and small upper skull like protohuman cave dweller
74 Triangular skull for pushing through the earth
75 Horn for pushing soil and fighting d4
76 Armoured skull and ridges over eyes but neck rigid and less mobile +1AC
77 Tusks for digging, curling hideously from skull d4 tusk if used to attack 
78 Wide snake or reptilian skull foot wide
79 No external ears, nose and eyes just slits, streamlined face for burrowing
80 Spikes on head ake harder to be eaten d3 damage per round to swallower
81 Glowing organs visible through skin
82 Organ produces vitamin D replacing need of sunlight
83 Richer hemoglobin reduces need for air 25%, more resistant to bad air
84 Transparent flesh and bones and most organs resemble glass
85 Multi chambered stomach with slower digestion -25% food required
86 Organs more mobile in body while moving or eating or damaged
87 Produce solid urea pellets reduce water needs by 25%
88 Blue copper based blood more efficient in extreme cold conditions
89 Can live without food for a month
90 Extra d3 hearts can survive if one killed, each extra heart is a extra HP
91 Phobic about open spaces
92 Phobic about light
93 When asleep parts of brain take turns to be alert to sensory threats
94 Brain highly resistant to oxygen starvation
95 Highly flexible sleep cycle can go without sleep two days a week
96 Pineal gland bursts through skull and can sense brain activity in 3"
97 Senses electrical activity in brains and nerves can fight in melee in dark within 1"
98 Sexually atracted to anything could remotely possibly have sex with
99 Threatened by reproductively viable members of same gender
100 Territorial loner only tolerates being close to mate occasionally, needs personal space

d100 Major Mutations

01 Sensitive to low frequency sounds in earth like burrowing, incoming quakes or cave ins

02 Magnetic sense used to navigate directions or sense magnetic fields
03 Tactile hairs can sense motion in the dark good enough to fight by up close within 1"
04 Smell food like mice or grubs or breath of nearby creatures through 1" dirt
05 Extreme low light vision but must have some dim light source at least to see
06 Sonar hearing like a bat by emitting sub sonic sounds used to see
07 Thermal crude b&w vision like adder as long as there are some temp variations
08 Antenna can smell food or sexual partners from up to two miles away
09 Streamlined face can breath under dirt if buried in loose dirt or rubble or burrowing
10 Sideways mouth allows flatter head for burrowing or pressure extremes
11 Luminescent skin shows patterns depending on emotions can dim when sneaking
12 Chitinous arthropod exoskeleton +2 AC
13 Skin highly lubricated by mucous +1AC and can easily escape bonds and wrestling
14 Skin seals rappidly if bleeding wounds below zero stabilize in one round
15 Skin tastes foul any monster biting must save before biting after first success
16 Skin has hallucinogenic mucous anyone biting or licking save or spend turn tripping
17 Skin is poison anyone biting or licking save or take d4+1/lv damage, can rub arrows on
18 Skin can be shed once a week over a turn recovering d6+1/lv HP
19 Chameleon skin changes colour and texture slowly to suit environment over a hour
20 Covered in spikes anything biting or attacking unarmed takes 1hp damage
21 Gills can breathe water
22 Only require 10% of oxygen
23 Can hold breath for 40 minutes
24 Chest covered in hard bony plastron like turtle +2AC
25 Limbs or tail regenerate over a month and can be snapped off if trapped
26 Regenerate 1HP/hour
27 Hump store three months food and a weeks water
28 Slow metabolism can reach negative CONx2 HP before death
29 Spine plates cause d3 damage to enemies using natural attacks from behind like bite
30 Skeletal structure with increased strength STR+1
31 Can digest stone and dirt, slow process but replaces normal food
32 Sensitive tail detects hostile movement from behind
33 Can emit foul musk when retreating or if bitten, enemy save or flees to avoid scent
34 Can leave sacks of sperm or eggs that survive for months till opposite sex uses
35 Any reproductive rivals with less HP save or become infertile after week near you
36 Urinate corrosive can dissolve 2d6 lb of limestone and weaken metal and other rock
37 Urine highly offensive to hostile scent sensitive creatures but attractive to opposite sex
38 Urine and feces glow for d6 days, can be used as lamps or sold as fake magic potions
39 Urine and feces highly nutritious and can be stored for a week before becoming foul 
40 Able to reproduce and hybridise with any animal or species
41 Fully functional extra set of arms and +1 ATT
42 Large claws d6 damage and +3" Burrowing speed (or 3 base if no burrow)
43 Gecko or frog like hand suckers can climb most surfaces and hang from ceiling
44 Sensitive fingers can detect seams like secret doors or feel vibrations through earth
45 Webbed hands allow swim speed of 50% ground (or 100% if web feet too)
46 Finger tips can taste and detect poison
47 Fingers have extra joint and double jointed improving any manual dexterity tasks***
48 Arms can retract into body cavity to reduce volume and fit in small spaces
49 Arms can extend up to 3 yards but become thinner and 1/2 STR at extreme reach
50 Hands are crab claws d6 damage each and extra attack if get again one claw is d8
51 Extra legs move +50% speed running speed
52 Feet can sense motion from ground like other beings walking/dig within 3"
53 Burrowing built feet add 3" to burrowing speed (or 3 base if no burrow)
54 Webbed feet allow swim speed of 50% ground (or 100% if web hands too)
55 Prehensile feet can be used as hands or weild a weapon (no extra att)
56 Bristles on legs sensitive to distant sounds range 24" like voices or metal tools
57 Cricket like legs can jump 3" once per round
58 Legs can retract into body cavity to reduce height and fit in small spaces
59 Legs can extend up to 3 yards but become thinner and 1/2 STR at extreme reach
60 Centaur like body configuration with four legs x2 MOV and ENC
61 Paralytic bite venom victim save or helpless for a turn and can be locked in larder
62 Huge snappy bite D6 Extra Attack
63 Tongue 3 yard long can swing from, grab things or small animals with a hit
64 Extendable second set of jaws shoot one foot out of mouth d6 damage extra attack
65 Vomit acid d4+1dam/lv three times a day 1" range/lv
66 Spit web like fluid once/3 lv/day, STR save to resist 3" range
67 Spit a bone bolt once/lv/day 12" range 2d4 damage need roll to hit
68 Spit flaming oil three times a day range 3" 2d6 automatic hit
69 Spit viral cocktail 3" once a day, victim saves or next offspring is hybrid with spitter
70 Spit diseased saliva 3" twice a day save of diseased and STR daily drops till cured 
71 Fighting horns d6 damage extra attack
72 Head can survive death of body, sprouts crab legs and grows a new body over a year 
73 Swollen head resembles glowing skull brain, can illuminate up to 6" radius at will
74 Armour plated skull +2AC like a organic or insectoid helmet
75 Filter face removes poison gas and has ten minutes reserve air once a day
76 Eye sockets extended providing 360 vision and hammer head face
77 Trunk yard long snout capable of holding objects, drinking water, feeding mouth with food
78 Huge sinus cavity for low frequency trumpeting heard over a mile away through earth
79 Skeleton becomes metallic, hard to break and +2AC
80 Bones can disconnect and change configuration into snake like thing for squeezing
81 Highly cold resistant can tolerate ice cold temperatures, blue blood -1dam/dice
82 Highly heat resistant can tolerate boiling temperatures, yellow blood -1dam/dice
83 Highly resistant to illness or fatigue +1CON
84 Highly efficient nervous system and reactions +1DEX
85 Immune to poison
86 Immune to disease
87 Adrenal boost once a day, x2MOV, +1ATT, one round/lv per day
88 Back up organs +d6+1/lv HP
89 Can labour or run for hour/CON point once per day, then save to remain concious
90 Adrenal Strength +d4 strength once a day, one round/lv per day 

91 Highly evolved preparedness and deep thought +1WIS
92 Enhanced Intellect +1INT
93 Parts of brain can take turns resting and can avoid full sleep for a week
94 Phenomenal spacial awareness can try ricochet missile shots with -2 to hit
95 Can see into ethereal plane 3"
96 Can see into astral plane with 3"
97 Electromagnetic sense detects life or neural activity with 9"
98 Pineal Gland pops through hole in head, sense life within 6", can bite like a snake for d4  
99 If eat brains can get flashes of memories and languages but forgotten in a hour
100 Superior insight into the minds of others +1CHA

d12 Apotheosis Third Stage Subterranean Mutations
1 Anyone you mate with fuses to body and shrinks away to just a face like tumour on skin
2 Devolve into a gelatinous slime like a ochre jelly
3 Devolve into a albino cave lobster with long limbs and glowing lure
4 Devolve into a immortal fungus that sinks into a quiet hole growing miles of huge roots
5 Devolve into a gibbering shoggoth
6 Devolve into a albino blind cave aquatic salamander and crawl into a well
7 Melt into a mass of eukaryotic slimy blob and ooze into the deepest depths
8 Melt and sink deep into the crust feeding off rocks, heat and radiation deep in the earth
9 Crawl into aquatic cave, turn into a giant transparent glass like water hydra rooted in place
10 Form cocoon in quiet place and hatch into a brood of albino mini clones a new race
11 Devolve into a giant albino cave slug
12 Sink into depths becoming a tentacled elder starspawn and join hive mind of your kind

This was handy for this and for my upcoming d100 parasite post
http://www.biologydiscussion.com/animals-2/adaptation/top-9-types-of-adaptation-in-animals-biology/59849

Previous Mutation Errata
Xorian Bio mutations and necro mutations got no taint tables
I guess that idea started with reptilians but was a good idea
One day all this will be together with my mutant character class.

 d12 Xor Mutation Taint Source
1 Exposed to parasites
2 Ate unprocessed infected tissue
3 Touched by highly infectious creature
4 Taint in bloodline for generations
5 Spattered with blood or bodily fluids of volatile mutant
6 Breathed some Xor spores
7 Biological weapon deployed
8 Biological weapon contaminated location long ago
9 Wicked person contaminated you deliberately via food
10 Had a contaminated lover
11 Almost drowned in biological matter
12 Exposed to damaged Xorian tissue weeping serum

d12 Necromutation Taint Source
1 Cursed by death god
2 Contaminated by contact with undead remains
3 Contaminated by cursed graveyard or haunted place over time
4 Food or water contaminated with undead
5 Caught a disease such as tomb rot
6 Bitten by necromutation tainted beast
7 Exposed to strange rays from a dark star or meteor
8 Wounded by weapon tainted with blood of a necromutant
9 Cursed by a dark relic or ghoul treasure
10 Made love to undead in disguise as a human
11 Made love to person undergoing necromutations 
12 Filthy undead contaminated your food or bed or clothes