The characters during the Iron God Adventure Path consistently get exposed to radiation, and in one adventure, in particular, they can potentially get exposed to mutagenic gasses either by drinking the Badwater in Iadenveigh or triggering a mutagenic gas release within the Aurora. I wanted to add a chance of there being a mutation but I didn’t want for it to be totally random and end up screwing up one of my players’ characters. I ended up lifting the methodology form Numenera setting which does a good job of risk vs reward. I have actually lifted a lot of good ideas from Numenera for this adventure path, cyphers and oddities for instance – so credit where credit is due.

MUTATION

When a character is exposed to radiation there is a 5% chance for each level of exhaustion incurred that a mutation occurs. Androids (and other inorganic life) are immune to this effect and creatures already with a mutation – like the Gamma Sorcerers – can choose to ignore the result. The PC has a choice as to the extent of the mutation effect but he can not choose the same mutation level if exposed again until he has selected all four options:

They may gain one beneficial mutation or
Three beneficial mutations with one harmful mutation or
One powerful mutation with one harmful mutation or
One distinctive mutation with one harmful mutation

A character may also roll for a cosmetic mutation for each mutation he gains – but this is optional. Only a wish or similar spell can remove mutations. Roll the appropriate number of percentile die on the below tables.

BENEFICIAL MUTATIONS

The following mutations do not require any visible changes or distinctions in the character. In other words, people who have these mutations are not obviously recognized as mutants. Using beneficial mutations never requires an action to “activate.”

01-05 Strengthened bones: You gain +1 to +2 to a physical attribute (STR, DEX or CON) determined randomly.
06-10 Improved circulation: You gain +1 to +2 to a physical attribute (STR, DEX or CON) determined randomly.
11-15 Improved musculature: You gain +1 to +2 to a physical attribute (STR, DEX or CON) determined randomly.
16-20 Improved nervous system: You gain +1 to +2 to a physical attribute (STR, DEX or CON) determined randomly.
21-25 Improved neural processes: You gain +1 to +2 to a mental attribute (WIS, INT or CHA) determined randomly.
26-30 Thick hide: You gain +1 to Armor.
31-33 Increased lung capacity: You can hold your breath for five minutes.
34-36 Adhesion pads: Your hands and feet have naturally adhesive pads and thus you gain advantage on checks for tasks involving climbing, keeping your footing, or retaining your grip.
37-39 Slippery skin: You secrete a slippery oil, giving you gain advantage on checks for any task involving slipping from another’s grip, slipping from bonds, squeezing through a small opening, and so on.
40-45 Telekinetic shield: You reflexively use telekinesis to ward away attacks, giving you an advantage on Dexterity saving throws.
46-50 Suggestive voice: Your voice is so perfectly modulated that it is you gain advantage on all Charisma based checks.
51-53 Processor dreams: When you sleep, you process information so that after you wake, you have advantage in any Intelligence actions held over from the previous day. For example, if you have to determine whether an unknown plant is poisonous, you could “sleep on it” and make the determination the next day with advantage on the check.
54-60 Poison immunity: You are immune to all poisons.
61-65 Disease immunity: You are immune to all diseases.
66-70 Fire resistance: You gain fire resistance.
71-75 Cold resistance: You gain cold resistance.
76-80 Intellect Fortress: You gain psychic resistance.
81-85 Acid resistance: You gain acid resistance.
86-88 Piercing resistance: You gain piercing resistance.
89-91 Slashing resistance: You gain slashing resistance.
92-94 Bludgeoning resistance: You gain bludgeoning resistance.
95-96 No scent: You cannot be tracked or located by scent, and you never have offensive odors.
97-99 Scent: You can sense creatures, objects, and terrain by scent as well as a normal human can by sight. You can detect scents with that degree of accuracy only in short range, but you can sense strong odors from much farther away (far better than a normal human can). Like a hound, you can track creatures by their scent. You gain advantage on Perception checks related to smell.
00 Sense Material: You can sense the presence of any single substance within short range, although you don’t learn details or the precise location. You and the DM should work together to determine the substance: water, iron, synth (plastic), granite, wood, flesh, salt, and so on. You do not need to concentrate to sense the material.

HARMFUL MUTATIONS

Unless noted otherwise, the following mutations are visible, obvious, and grotesque. They offer no benefits, only drawbacks.

01: Arm drops off and crawls away
02: Eyes implode (4d8 points of damage and blindness)
03: Stomach climbs up esophagus and serves as an external organ (-4 Charisma)
04: Head enlarges to five times its normal size (victim suffers severe headaches that inflict a -2 penalty on all die rolls)
05: Vocal cords atrophy (victim cannot speak)
06: Body requires 2 quarts of blood per day to survive
07-10 Deformed leg: You lose 10’ of movement and all checks related to movement have disadvantage.
11-20 Deformed face/appearance: You have disadvantage on all Charisma based checks.
21-30 Deformed arm/hand: All checks related to your arms or hand (most likely Dexterity and Strength) have disadvantage.
31-40 Malformed brain: You have disadvantage on all Intelligence checks.
41-45 Mentally vulnerable: You have weakness to psychic damage.
46-50 Slow and lumbering: Your speed is halved and you have disadvantage on Dexterity based checks.
51-60 Sickly: You have disadvantage on all Strength based checks.
61-63 Horrible growth: A large goiter, immobile tendril, or useless extra eye hangs from your face, increasing the difficulty of all pleasant interactions. You have disadvantage on all Charisma based checks.
64-66 Useless limb: One of your limbs is unusable or missing.
67-71 Useless eye: One of your eyes is unusable or missing. You have disadvantage on Perception checks involving sight.
72-76 Useless ear: One of your ears is unusable or missing. You have disadvantage on Perception checks involving sight.
77-84 Weakness in Might: You gain a permanent -2 to your Strength ability score.
85-92 Weakness in Speed: You gain a permanent -2 to your Dexterity ability score.
93-00 Weakness in Intellect: You gain a permanent -2 to your Intelligence ability score.

POWERFUL MUTATIONS

The following mutations do not require any visible changes in the character until used. People who have these mutations are not obviously recognized as mutants if they don’t use their powers. Using some of these mutations costs an action.

01 Heightened Attribute: A random Ability Score raised by 2 points, to a maximum of 30.
02 Weapon immunity: Immune to normal weapons and attacks by creatures of less than CR 4.
03 Magic resistance: You have advantage on your saving throws against magical effects.
04 Energy attack: Once per day attack inflicts 3d10 points of energy damage on one target; must originate from caster. You pick the energy type when you gain this mutation.
05 Clairaudience: As the spell 3 times per day.
06 Mind blast: As the illithid power, once per day.
07 Darksight: You gain darkvision out to 120 feet.
08-10 No breath: You do not need to breathe.
11-15 No water: You do not need to drink water to survive.
16-20 Chameleon skin: Your skin changes colours as you wish. This gives you advantage on Stealth checks.
21-24 Savage bite: Your mouth widens surprisingly, and hidden, pointed teeth emerge when you wish it. You can make a bite attack as a bonus action that inflicts 1d6 points of damage.
25-26 Gluey globs: You can produce gluey globs at your fingertips. You gain advantage on tasks involving climbing or keeping your grip. You can also fling these globs up to 30 feet, and if they hit, they target gains disadvantage on any Strength or Dexterity based ability checks. Bonus action to use as an attack.
27-30 Face dancing (3/day): You can alter your features enough that you can disguise yourself more easily. This works as the disguise self spell.
31-35 Sense technology: You can sense the presence of a functioning tech device or effect within short range. You do not learn details or the precise location. Uses a bonus action.
36-40 Stinger in finger: You can make an attack with your hand that inflicts 1d6 point of damage. On a successful hit, your stinger also injects a poison that inflicts the poison status on the target if they fail a DC 10 Constitution saving throw. Uses a bonus action.
41-44 Stinger in elbow: You can make an attack with your elbow that inflicts 2d6 points of damage. On a successful hit, your stinger also injects a poison that inflicts the poison status on the target if they fail a DC 10 Constitution saving throw. Uses a bonus action.
45-47 Spit needles: You can make an attack within 5 ft. against one target. You spit a needle that inflicts 1d4 point of damage. On a successful hit, your needle also injects a poison that inflicts the poison status on the target if they fail a DC 10 Constitution saving throw. Uses a bonus action.
48-50 Spit acid: You can make an attack with 5 ft. against one target. You spit a glob of acid that inflicts 1d4 points of damage. Uses a bonus action.
51-53 Spit webs: You can make up to 10 feet of a strong, ropelike material each day at the rate of about 1 foot per minute. You can also spit globs of webbing in within 5 ft. range, and if they hit, they act as the web spell except where noted.
54-59 Filtered lungs: You have advantage on Constitution saving throws against vapours or noxious gases. You can survive in a hostile breathing environment (such as underwater or in a vacuum) for up to ten minutes.
60-62 Disruptive field (electronics) (2/day): When you wish it, you disrupt devices within 10 ft. sphere (no roll needed). All devices operate as if they were timeworn and roll on the glitch table on their next shot. Devices while in the field that use their last charge cannot be recharged. Uses a bonus action.
63-65 Disruptive field (flesh) (2/day): When you wish it, you disrupt flesh within 10 ft. sphere. All creatures within range of your field must make a DC 15 Constitution saving throw or gain one level of exhaustion. Uses a bonus action.
66-68 Disruptive field (thoughts) (1/day): When you wish it, you disrupt thoughts within 10 ft. sphere (immediate) range. All intelligence, Wisdom and Charisma ability checks and saving throws have disadvantage. Furthermore, spellcaster must make a concentration check whenever they cast a spell or lose the spell. Uses a bonus action.
69-70 Magnetic flesh: You attract or repel metal when you desire. Not only do small metal objects cling to you, but this mutation is an asset in tasks involving climbing on metal or keeping your grip on a metal item granting you advantage. This mutation is an asset to your defence when being attacked by a metal foe or a foe with a metal weapon who gains disadvantage on the roll against you.
71-73 Gravity negation (2/day): You float slowly into the air. If you concentrate, you can control your movement at half your normal speed; otherwise, you drift with the wind or with any momentum you have gained. This effect lasts for up to ten minutes. Otherwise, it works as the levitate spell. Action to initiate.
74-80 Telepathy: You can speak telepathically with others who are within short range. Communication is two-way, but the other party must be willing and able to communicate. You don’t have to see the target, but you must know that it’s within range. You can have more than one active contact at once, but you must establish contact with each target individually. Each contact lasts up to ten minutes. You may spend an inspiration (or Fate Point) to increase the duration to 28 hours. Action to establish contact.
81-85 Pyrokinesis: You can cause a flammable object you can see within immediate range to spontaneously catch fire. If used as an attack, this power acts as the firebolt spell. Uses a bonus action.
86-90 Telekinesis (2/day): You can exert force on objects within short range. This acts as the telekinesis spell. Uses a bonus action.
91-92 Phaseshifting (2/day): You can pass slowly through solid barriers. This acts as the passwall spell. You can’t pass through energy barriers. Uses a bonus action.
93-94 Power device (1/day): You can charge an artifact or other devices, even timeworn devices so that it can be used once. You can do this once a day or spend a Fate Point per device charge. This is a bonus action.
95-96 Drain power: You can drain the power from an artifact or device, allowing you to regain 1 hit point per charge of the device. You regain hit points at the rate of 1 point per round and must give your full concentration to the process each round. Action to initiate; action each round to drain.
97-99 Regeneration: In addition to regaining points through normal recovery rolls, you regenerate 1 hit point per hour, regardless of whether you rest, until you are at your maximum.
00 Feed off pain: Any time a creature within immediate (10 ft.) range suffers at least 10 points of damage in one attack, you can restore 1 hit point, up to its maximum. You can feed off any creature in this way, whether friend or foe. You never regain more than 1 point per round.

DISTINCTIVE MUTATIONS

The following mutations involve dramatic physical changes to the character’s appearance. People who have these mutations are always recognized as mutants. Using some of these mutations costs an action.

01-04 Extra mouth: You have an extra mouth on your hand, face, or stomach. This mouth is filled with razor-sharp teeth and, if used to attack, inflicts 1d6 points of damage. You can also speak with two voices at once.
05-08 Snakelike arm: One of your arms ends in a fanged mouth. You can use it to attack, Inflicting: 4 (1d4 + 2) piercing damage plus 14 (4d6) poison damage. You can’t use the snakelike arm for anything other than biting.
09-12 Tendrils on forehead: Four to six tendrils, each 12 to 24 inches (30 to 61 cm) long, come out of your forehead. They can grasp and carry anything that your hand could, although a large object would block your field of vision. Also, roll on the beneficial mutations list.
13-16 Tendrils instead of fingers: Your fingers are tendrils 12 inches (30 cm) long. They grant you advantage to any task involving climbing, grasping, or keeping your grip. Further, you can effectively pick up and hold two objects in each hand rather than one. You can’t wield more than one weapon per hand. Also, roll on the beneficial mutations table.
17-20 Tendrils instead of arms: Your arms are tendrils 6 feet (1.8 m) long (or only one arm is a tendril if you prefer). Although you lose the fine manipulative ability of fingers and a thumb, you can still grasp objects, have a much longer reach (10 ft.), and gain advantage for all tasks involving grappling or wrestling. Also, roll on the beneficial mutations table.
21-23 Tendrils instead of eyes: You are blind, but each eye socket has a retractable tendril that is 10 feet (3 m) long. These tendrils can feel around rapidly to give you a physical sense of everything within immediate range. Further, they can be used to manipulate very light objects, activate controls, and so forth. Also, roll on the beneficial mutations table.
24-26 Tendrils instead of legs/feet: Your legs or feet are tendrils that are 6 feet (1.8 m) long (or only one leg or foot is a tendril, if you prefer). You can still walk and move normally, and you gain advantage on all tasks involving grappling or wrestling. The tendrils are prehensile enough to grasp large objects. Also, roll on the beneficial mutations table.
27-32 Scaly body: You gain +2 to Armor Class.
33-36 Covered in spiny needles/spikes: Any creature striking you with its body automatically suffers 5 points of damage.
37-39 Quills: You have quills that you can launch from your body to attack a foe within 30 feet range. This attack inflicts 6 (1d8 + 2) piercing damage, and you never run out of ammo. You can also use this attack in melee. Uses a bonus action.
40-44 Carapace: You gain +2 to Armor.
45-49 Chlorophyll: You gain nutrients from the sun and don’t need to eat or breathe if you have daily exposure to sunlight. Your skin, not surprisingly, is green.
50-54 Extra joint in arms: Your arms are long and jointed so that you have two elbows in each. You have a long reach and can strike foes from unexpected angles. This mutation grants advantage when making melee attacks.
55-59 Extra joint in legs: Your legs are long and jointed so that you have two knees in each. You have a long stride (+10 feet of movement), and this mutation grants advantage for all running, climbing, jumping, and balancing tasks. Also, roll on the beneficial mutations table.
60-62 Spider legs from torso: In addition to your normal limbs, six or eight spiderlike legs, each 6 feet (1.8 m) long, extend from your sides. They grant advantage on any task-involving running, keeping your feet, standing your ground, and climbing. Also, roll on the beneficial mutations table.
63-67 Extra arms: You have one or two extra arms. They can hold objects, wield weapons, hold a shield, and so on. This mutation does not increase the number of actions you can take in a round or the number of attacks you can attempt.
68-70 Extra legs: You have two extra legs. They grant advantage on any task involving running, keeping your feet, and standing your ground. Also, roll on the beneficial mutations table.
71-73 Spider legs: Instead of normal legs, you have a wide torso with six or eight spiderlike legs. They grant advantage on any task involving running, keeping your feet, standing your ground, and climbing. Also, roll on the beneficial mutations table.
74-78 Snake tail: You have a prehensile tail that is 6 feet (1.8 m) long. It grants advantage for all tasks involving grappling or wrestling. The tail can grasp large objects. Also, roll on the beneficial mutations table.
79-80 Snake tail instead of legs: Instead of legs, you have a snaky tail that is 8 feet (2.4 m) long. You move at the same speed and gain advantage for all tasks involving grappling or wrestling. The tail is prehensile enough to grasp large objects. Also, roll on the beneficial mutations table.
81-85 Stinging tendril: You have a prehensile tendril (or tail) that grows from some part of your body and ends in a poisonous stinger. You can make an attack with your stinger that inflicts 2d6 + STR piercing damage. The target must make a DC 15 Constitution saving throw, taking 12 (3d6) poison damage on a failed save, or half as much damage on a successful one. The tendril (or tail) can’t be used for anything else. Uses a bonus action to attack.
86-90 Eyes on stalks: Your eyes are on stalks and can move in any direction, independently of each other. You can peek around corners without exposing yourself to danger. This is grants advantage on initiative and all Perception checks that rely on sight. Also, roll on the beneficial mutations table.
91-92 Extra eyes on hands/fingers: You can peek around corners without exposing yourself to danger. This is grants advantage on initiative and all Perception checks that rely on sight. Also, roll on the beneficial mutations table.
93-97 Aquatic: Your body is streamlined and finned, your fingers and toes webbed. You gain a swim speed of 50 feet. You also have advantage on tasks related to swimming (including underwater combat, tracking etc.), and you can see perfectly underwater (as if above water). Although you have lungs, you also have gills, so you can also breathe underwater.
98-00 Wings: You have feathered or fleshy wings and gain a fly speed of 50 ft.

COSMETIC MUTATIONS

Distinctive mutations affect nothing but the appearance of a character. None is so pronounced as to make a character decidedly more or less attractive. They are simply distinguishing alterations.

01-02 Purple skin
03-04 Green skin
05-06 Red skin
07-08 Yellow skin
09-10 White skin
11-12 Black skin
13-14 Blue skin
15 Purple hair
16 Green hair
17 Red hair
18 Yellow hair
19 White hair
20 Blue hair
21 Striped hair
22 Horns
23 Antlers
24 Extremely hirsute
25 Entirely hairless
26 Scaly skin
27 Leathery skin
28 Transparent skin
29 Skin turns transparent in sunlight
30 Skin changes colour in sunlight
31 Very tall
32 Very large
33 Very short
34 Very thin
35 Very long neck
36 Hunched back
37 Long, thin tail
38 Short, broadtail
39 Long arms
40 Short arms
41 Long legs
42 Short legs
43 Bony ridge on face
44 Bony ridge on back
45 Bony ridge on arms
46 Purple eye(s)
47 Red eye(s)
48 Yellow eye(s)
49 White eye(s)
50 Black eye(s)
51 Large eyes
52 Bulbous eyes
53 Two pupils in one eye
54 Large ears
55-56 Pointed ears
57-58 Webbed fingers
59-60 Webbed toes
61-62 Four fingers on each hand
63-64 Six fingers on each hand
65 Long fingers
66 Purple nails
67 Green nails
68 Yellow nails
69 White nails
70 Black nails
71 Blue nails
72 Odd lumps on flesh
73 Useless antennae (like an insect)
74 Extra useless limb
75 Extra useless eye
76 Fleshy frills or useless flagella (small)
77 Useless tendrils (large)
78 Mandibles
79-80 Pointed teeth
81 Tusks
82 Black teeth
83 Red teeth
84 Purple teeth
85 Green teeth
86 Purple lips
87 Green lips
88 Yellow lips
89 White lips
90 Black lips
91 Blue lips
92 Purple spittle
93 Red spittle
94 Yellow spittle
95 White spittle
96 Black spittle
97-98 Distinctive odor
99 Feathers
00 Head crest

Banner Art Credit.

MUTATIONS