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Mutations act much like traits, in that they give your character a variety of passive effects. Unlike traits, which can be selected upon creating a new character, mutations can only be obtained in-game and are somewhat random. Like traits, mutations can be both beneficial and harmful to your character.

Does it hurt?

Chart of mutations dependencies (outdated, but good starting point) (PNG version, SVG version)

Yeah, sometimes. Mutations can be obtained by consuming some questionable products (mutagens, Mutagenic serums, misshapen fetuses, arms, legs and sewage samples), romping through radioactive areas, and other unhealthy methods. There is 2/3 chance to have any mutation and 1/3 chance to have only a "bad" mutation, though not all "bad" mutations are really bad ones and not all "good" mutations are equally desirable. Also, check Robust Genetics trait, which changes chances drastically. It flips the 1/3 chance to have only a "bad" mutation to a 1/3 chance to have only a "good" mutation.

If you end up with unwanted mutations a purifier can (usually, some cannot be purified) help purge them. It can revert up to four mutations (this chance is higher if you have a lot of mutations). Purifier seeks to return you to your fresh-from-chargen status, so it won't remove negative traits you took at the outset. Be advised that there are some traits which Purifier can't touch, though...

Even if there is no forced "bad" mutation, chances are not equal for all traits. Mutations are split up into a dozen categories and even more trees. Trees have various requirements for the different branches and most branches being opposed to one another. The more branches are opened up, the less likely a new branch or a categorized mutation will be gained, with the game prioritizing current upgrades to everything else. Direct upgrades have the most priority, with a (5/(number of available upgrades + 5)) chance to be skipped, then mutations from a category pool, and only then game picks random mutations from the full list of all mutations.

Once the code determines what trait you're due to get (generally based on mutation category: either your strongest one or what you opted to use), it then starts mutating you in that direction. Since it can pick traits for which you haven't got the prerequisites, the code will then downshift and give you the most relevant trait you can obtain.

For example, if TRAIT_$LETTER needs the preceding letter (B needs A, C needs B, and so on) and the code goes for C, it'll give you C if you have B, B if you have A, and A if you don't have any of them. If you used something that gives more than one mutation in one go, there's no guarantee that the next mutation will then continue the chain. Sometimes it happens. Sometimes it doesn't--that's how mutations work!


While most mutations are passive and are thus constantly in effect or conditionally triggered, a small number manifest as active abilities and can kick in on demand; some will self-trigger by random chance. Like bionics, player-initiated use of these mutations has a use cost, and most of them add their corresponding cost(s) to your hunger, thirst or fatigue level. At certain caps, however, the action will instead be canceled (or interrupted), such that you cannot kill yourself by using your mutations. Hunger caps at 700 (between Famished and Near starving), thirst at 260 (a bit over Dehydrated), and fatigue at 575 (Exhausted).

To access the mutations menu, which can be use to toggle mutations or activate them use the { key.


Traits tend to provoke other mutations from the same category: your genetic and biochemical makeup is shifting.

When you mutate, the game checks your mutations and notes which category is most strongly represented. There is a (strength/total_strength) chance that a random mutation will be chosen from this category. If it fails this test (due to amount of traits-outsiders), or there are no more mutations in the category, then a random mutation is selected, without any linkage to categories at all. Every in-category trait gives 8 points to its category's strength. Every not-in-category trait takes away one point from each rival category unless that category already has strength 0 or passes a 1/strength check.

Once a mutation is selected, you will begin to mutate towards it. If any mutations you currently have conflict with this mutation, then one of the conflicting mutations is randomly removed. If you have no conflicting mutations, but don't have any of the prerequisites, you will begin to mutate towards a random prerequisite. If you already have a prerequisite mutation and no conflicting mutations, you gain the selected mutation immediately.

There are quite a few different categories, each providing a different type of experience when mutated into:

  • Lizard: A relatively "balanced" melee-centric mutation. Reduced dexterity and cold blood in exchange for some decent combat and utility mutations.
  • Bird: Very mobile in exchange for poor health and defense. You're faster than a Kenyan on PCP and have no need for things like "shelter" or "regular meals", but all it takes is a couple of good hits to kill you.
  • Fish: This should be obvious, but Fish mostly just makes you really good at swimming.
  • Beast: The opposite of Bird. Amazing in close combat, but extremely high-maintenance.
  • Feline: Basically just a catlike variant of Beast.
  • Lupine: Basically just a doglike variant of Beast.
  • Ursine: Another slow-moving melee tank. Exists mostly as an excuse to add the hibernation mutation.
  • Cattle: You're a huge, lumbering herbivore with a lot of health, a powerful natural attack and the ability to eat bushes. Plays like a less restrictive version of Plant.
  • Insect: Fairly capable melee-centric mutation. It's not as potent as Lizard or Beast, but it also has fewer drawbacks. And it comes with a few utility mutations to boot.
  • Plant: You're a slow, thorny tank that uses very little in the way of supplies. Great for turtling, not so great for raiding dungeons.
  • Slime: Chaotic. Offers both great boons (many of them situational) and catastrophic drawbacks. Comes all down to Luck.
  • Troglobite: You turn into a underground nightcrawler. It has a lot of nasty side effects like making you useless in the daytime.
  • Cephalopod: Surprisingly flexible. Adapts quickly to most situations, be that melee, swimming or stealth. If you get there that is, which will take you a while.
  • Spider: You make webs, move fast and have a poisonous bite.
  • Rat: Produces a durable but very high maintenance character. Requires you to look for new food constantly.
  • Medical: Become invincible to anything but a shotgun in your face, with minimal drawbacks. Who needs doctors and bandages anyway?
  • Alpha: A very "safe" category. Low risk, low reward. A next step in human 'evolution'.
  • Elf-A: A lot like Chimera, except stealth-based instead of combat-based.
  • Chimera: Super-Beast. You have pretty much every good offensive mutation, but you also have a ton of negative mutations and will probably die after a few days.
  • Raptor: High speed predator. Somewhat like an assassin goes quickly into melee, kills and can flee fast on the first sign of danger. Not as durable as other melee mutations though.
  • Mycus: Play around with fungus to get this. You are now part of the fungal invasion of earth. Traitor!. Not obtainable using normal mutagens. Locks you out of other mutations.
  • Marloss: Eat Marloss Berries, Marloss Seeds, and Marloss Jelly to get this..

For a complete overview, see List of mutations.


Though most mutations are more or less surface-only (and can be reversed with Purifier) they do affect you whilst they're present. If you use particularly strong doses of targeted mutagen and are already strongly involved in that category, you may permanently transcend your humanity. This is known as "crossing the Threshold". Becoming post-human unlocks further mutations which offer radical alterations to your character's body and mindset. At this point, the only disadvantage to crossing a threshold is that it bars you from crossing others.

Thresholds under the hood

You can only cross a Threshold with injectable mutagen. No matter how many gallons of mutagen you drink, drinking mutagen won't do the job. (That may change later, but it's not a major priority.) In order to be eligible to obtain a Threshold mutation, the character must:

  • not have any Threshold mutations (denoted by the threshold boolean set true in mutations.json, and currently all designated THRESH_$CATEGORY for clear reference/sorting)
  • have reached third-tier mutation dreams (they occur often and are fairly specific)

At this point, you need to be injecting mutagen specific to your strongest category. If you dream of chasing rats, for instance, you're third-stage Feline. If you meet the above criteria, injecting Feline mutagen will have the usual effects, and then roll to see if you breach the threshold.

The roll is a straight "x in y" roll: your strength in your chosen category over your strength in ALL categories. If, to continue the example, you really wanna be a cat and use exclusively Feline mutagens, two or three injections, if you get all three mutations from each, might do the job. If you spread your mutations around and try different categories, it'll take more effort and more mutagen to breach a Threshold.

Certain messages come up related to thresholds.

  • "You feel something straining inside you, yearning to be free" indicates that the mutation process tried to give you a post-Threshold mutation but you didn't have the Threshold required. Your humanity is resisting!
  • The various headaches that can come up happen when you're particularly strong in a category and tried for a Threshold, but you missed the roll. Your humanity resisted turning into a mutant creature!


Mutating can feel good. It can make you feel great ... Smarter ... More aggressive, like you could TAKE ON THE WORLD! As such, they can be quite addictive. Purifier, with potentially greater effects, is even more addictive. Serums, being concentrated, are worse still.

Please use mutagen responsibly.

Sources of mutation

Here are various ways you can get mutated after character creation. Some mutations are only obtainable on character creation, these are listed on the wiki as "Not a valid random mutation" in the mutation information box. Any others can be acquired via mutations, some might require special items the marloss mutations, or special serums, for the Threshold mutations.

Targeted mutations

Not all mutations are valid mutation targets when being mutated. Some can only be chosen at character generation, and others require a specific threshold. Others cannot be randomly mutated at all, these will be listed as 'Targeted Mutation Only' on their mutation pages. This means you can only get them from mutation sources that have this mutation in their threshold list. For example, you cannot get schizophrenic from normal mutagen, but you can get it from medical mutagen.

See also