So since I DM a campaign heavily inspired by the Warhammer World, I thought "What is Warhammer without some mutations."

What creature in its right mind would like one of these mutations aside from the unhinged servants of the Dark Brothers? Well maybe a character that unfortunately attunes to a weapon with the Boon of Mutation trait that will force a single, permanent Mutation upon them. Or a character that attunes to a weapon like that taking a chance in hoping to get summin good. 

I created this boon to throw in some customization for my hostile NPC's that are part of the servants of darkness. You can adapt and change this table however you want, and I would recommend giving the stronger boons to special NPCs or something if that is somehow of interest to you. It is also more a draft currently and still needs some looking at, but is less meant for hero characters but more for your "Dark, Evil and Edgy™" NPCs or evil oneshot PC's. Currently I use this boon on magic items in possession of the mentioned NPCs so as to have a rule on what creatures have those mutations and marking them as stronger than normal creatures.

Have fun with it, and never forget: Change what you want, it is your world.

• • 1-3: Your Skin is covered in root-like growths in shimmering colors. You gain +1 to your AC, but your Charisma is reduced by 1
  • 4-6: You grow an additional appendage underneath one of your arms. Roll 1d4: 1. Crustacean 2. Reptile 3. Tentacle 4. Normal arm pertaining to the characters race
  • 7-9: An enormous horn grows out of you head right above your eye. It can be used as part of an attack action to deal an additional 1d4 piercing damage
  • 10-12: Once per Long Rest, after hitting 0 Hit Points and not dying outright, you come back to 1 Hit Point instead in a flash of black whirling mist and purple light.
  • 13: Your organs grow outside of your body. No one knows how a creature like this can survive, but the unnatural energies of Chaos seem to work in confusing ways. The creature suffers vulnerability to all damage.
  • 14-17: Your skin becomes translucent and your eyes turn milky white
  • 18: The fabric and composition of your mind and thought processes change dramatically. When making an Intelligence Ability Check the Intelligence is swapped out with Charisma and vice versa.
  • 19-20: Roll 1d4. On an odd number your grow twice your size and become one size category larger than you were before. On an even number you shrink to half your size and become 1 size category smaller
  • 21-23: One of your hands turns into an animalistic claw and fur grows up to your shoulder
  • 24-26: You grow a second row of teeth, like an additional mouth within your mouth
  • 27: Your sex changes to the opposite
  • 28-30: Your lower body transmutes into that of a different form, essentially turning you into a pseudo-centaur. Roll 1d4: 1. Snake (advantage on Stealth Checks) 2. Spider (permanent Spiderclimb) 3. Quadrupedal (increase movement speed by 20 and size by 1 category) 4. Aberration (Tentacles, pods that cause trypophobia, etc. Gain Hover Speed equal to your movement speed)
  • 31: Your body swells, flesh rots, your innards spill forth from your broken stomach and your weight triples and you become a living resemblance of Nurghul. Your become immune to disease and you gain 5 Hit Points for every Level you have, however your appearance and stench is almost unbearable to every living creature close to you
  • 32: You grow a double-pair of wings. Roll 1d4: 1. Moth 2. Bat 3. Angel 4. Bones. These wings give you a flying Speed of 30 feet
  • 33-36: Your elbows and knees break and your appendages elongate and thin out, making your physical appearance eerily out of proportion
  • 37-39: Your lungs change. Roll 1d4: 1. You can breath water 2. Gases and gaseous poisons don't affect you 3. You can hold your breath for 8 hours 4. You are immune to suffocation
  • 40: You become connected to the primordial truth. Once per week you can cast Divination based on Wisdom and the source of the answers is the metaphysical realm of thought and emotion. But be weary of what lurks in the depths
  • 41-42: You grow a tail with a stinger. Roll 1d4: 1. Scorpion 2. Wyvern 3. Snail 4. Spine. As an action you can make an attack with that stinger. Depending on the Stinger the tail has a different effect: Scorpion: Poisoned for 1 minute. Wyvern: Paralyzed until start of next turn. Snail: Suffers 2d8 Poison Damage. Spine: Becomes grappled and incapacitated, reach increases to 20 feet
  • 43-44: You gain an additional Organ, which increases one of your Ability Scores by 1. Roll 1d6 to determine which Ability Score.
  • 45: If you cast a Spell and it is countered by Counter Spell, you suffer a seizure until the start of your next turn and become paralyzed because of that. However, you do not lose your Spell Slot.
  • 46-49: Your head sinks into your chest. Your armor needs to be retrofitted, but other than that you suffer no additional effect besides a hideous appearance
  • 50: The Flesh of your skull burns away and your head becomes a burning skull. Once per Long Rest you can cast Fear with a DC of 15
  • 51-53: One of your wounds, that is either scarred or relatively fresh, is now filled with a myriad of eyeballs. You increase your passive perception by 1, but whenever you are targeted by the Blindness Spell you have disadvantage on the saving throw.
  • 54-55: Your face becomes featureless, a blank slate of skin. You do not need to eat or drink, but your senses still work as normal and you can talk normally even though you don't have a mouth.
  • 56-58: One of your arms doubles in size and gains a second elbow-joint. If you carry a weapon with that Arm it gains an additional 5 ft. reach
  • 59-62: You grow a second mouth. Roll 1d4: 1. Center of your Forehead 2. Stomach 3. Palm of your hand 4. Back of your head. It functions like a normal mouth
  • 63: Your body becomes emaciated, but your mind sharp as never before. Your Strength, Dexterity and Constitution is reduced by 2, but your Intelligence, Wisdom and Charisma is increased by 2.
  • 64-65: Your eyes change color and stare deep into the soul of a living being. Once per Short Rest you can cast Detect Thoughts, based on Charisma.
  • 66-68: Your hands grow 1d4 additional fingers.
  • 69-70: You become a living icon of blasphemy. Roll 1d6 to determine an ability score after every long rest. Creatures within 30 feet of you have disadvantage on ability checks and saving throws based on that ability score.
  • 71: You are filled with unnatural and chaotic powers. Once per Short Rest you can cast Chaos Bolt based on Intelligence at third Level without expending a Spell Slot
  • 72: One of your arms transforms into a natural weapon, comparable to a great sword in size and damage. After the elbow, the arm appears like a twisted, elongated, thin but 5 foot long mouth filled with a row of teeth and is adorned by sharp, jagged blades. The mutation ends roughly at the shoulder, where bones jut through the skin like spikes. The weapon deals 2d6+ strength modifier slashing or piercing damage, depending on if the character wants to strike with the blades or open the mouth to bite.
  • 72-73: Your body fuses with your plate armor. If you don't wear any plate armor, over time, your body produces metal plating similar to plate armor, however heavily adorned by the symbols of the dark gods. This armor does not have a strength requirement but will take time to grow. The armor starts with an AC of 14 for the first Tier. For every Tier the AC increases by 1. For the purposes of Spells you count as wearing armor. If the AC reaches 16, there are enough plates to cause disadvantage on stealth checks, and if the AC hits 18, your entire body is covered in mighty metal plates, only the glow of red eyes coming from underneath the helmet and the heavy breath of a creature trapped within a sarcophagus fused with its own body. This process does not halt, except with a greater restoration spell, upon which the armor falls to the ground and the body is free again.
  • 73: Your muscles swell to an unprecedented size. Your Strength becomes 23, but your dexterity is reduced by 4
  • 74-76: One of your limbs turns into that of another creature. Randomly determine one of your arms or legs and roll 1d4: 1. Reptilian 2. Insectoid 3. Mammalian 4. Avian
  • 77: Your strikes are accompanied by an aura of pure hate projecting outwards to those creatures you are assailing. If you land a critical hit with a ranged, melee or spell attack, the creature is afraid of you until the end of its next turn.
  • 78-80: Your blood is substituted with a different material. Roll 1d4: 1. Poison 2. Fire 3. Acid 4. Force. If a creature hits you with an attack, it suffers 1 point of damage + your constitution modifier according to the type of blood you carry in your veins.
  • 81-83: You are marked with an ever burning Sigil on your chest. It might be a symbol connected to your past or a symbol connected to the dark gods themselves. Increase your Charisma by 1 and reduce your Constitution by 1
  • 84-87: Your stomach acid becomes lethal and potent. As an action, once per Short Rest, you can target a creature or object within 30 feet of you and make an attack roll based on Dexterity. On a hit the creature suffers 2d10 acid damage and is blinded until the start of its next turn. An object made of mundane metal that is not larger than 5 cubic inches is immediately destroyed. Otherwise it has an unpleasant marking on its surface.
  • 88-90: You receive a weapon made of the stuff chaos. Roll 1d4 to determine which god it is derived from: 1. Khorne 2. Nurghul 3. Tzeentch 4. Slaanesh. The Weapon appears as a form of sword, maul or hammer, however the damage is the same. The weapon deals 1d12 + strength, dex or charisma modifier Force Damage. The character is proficient with it.
  • 91: Your senses become overloaded and you become capable of sensing even the tiniest details. You increase your passive perception and investigation by 5, but suffer vulnerability to thunder damage and radiant damage
  • 92-93: Your body becomes malleable like jello. You can pass through gaps as narrow as 1 inch.
  • 94-96: You gain the ability to speak, read and understand every language, but lose the ability to speak, read and understand Common
  • 97-98:You become like a shadow, whispy like mist. You gain advantage on stealth checks. Once per Short Rest as Bonus Action you can teleport from one dim place to another one within 60 feet.
  • 99: You become connected to a place of your past or future. Once per Week as an Action you can teleport to that place, no matter on what plane of existence you are. 1 minute after teleporting you can teleport back to where you started.
  • 00: Your soul fuses with the very essence of the object causing the mutation. You are no longer attuned to it and its abilities and attributes become inherent to yourself. If the mutation was not caused by an Object, role again.

This is awesome! Do you have anything else like this?

Thank you! My dm used this and it's alot of fun