Fallout 76 mutations

General information
Mutations are a type of condition in Fallout 76.

When the player character gets exposed to radiation, they have a 5% chance per 5 HP radiated to be mutated. This can occur from being struck by excessive background radiation from an source such as zones devastated by nukes, irradiated creatures, radioactive waste etc., or by consuming radioactive food and liquids. A player character can have multiple mutations at once.

RadAway has a chance to cure a random mutation, while any radiation protection gear (e.g. hazmat suit or gas mask) reduces the chance of mutation. The Starched Genes perk will also prevent mutation but will prevent RadAway from curing acquired mutations, essentially making them permanent while the perk card is equipped. Entering a contamination chamber will cure the radiation thus removing a random mutation.

Mutations are retained when the player character dies and respawns, however a small percentage of the accumulated rads are eliminated each time a death occurs. If the player character does not yet have the Starched Genes perk and are attempting to keep a desirable mutation, one can simply avoid using RadAway and allow oneself to be killed repeatedly if needing to eliminate excessive accumulated rads (such as falling from a cliff).

Mutations are like traits from Fallout: New Vegas in that they have both positive and negative effects, such as the Strange in Numbers perk, which will increase the positive effect of a player character's mutation by 25% when their teammates are also mutated. The Class Freak perk can also reduce the negative(s) by up to 75%, though does not diminish the effects of diseases with the Plague Walker mutation. However, some of the diseases can have their effects diminished by perks (increased hunger due to parasites via Happy Camper or All Night Long, increased limb damage via Adamantium Skeleton, etc.).

The mutations Herbivore/Carnivore are mutually exclusive and cannot be obtained simultaneously.

Serums
Mutation serums can be purchased from The Whitespring bunker once the player character joins the Enclave. The MODUS science terminal vendor found in the Science Wing of the bunker, the serums available are random and located in the Aid section. The base cost is 5,000 caps.

Buying multiple of the same mutation serum from the Whitespring bunker does NOT stack the mutations, but instead gives the player a buff of "Suppresses negative mutation effects" for one hour. For example, purchasing a marsupial serum and consuming it while you already have the Marsupial mutation will remove the intelligence debuff.

Mutation serum recipes can be purchased from the Whitespring bunker as well, once the player character joins the Enclave. The MODUS science terminal vendor can be found in the Science Wing of the bunker. The serum recipes have a base cost of 20,000 caps.

Prior to Fallout 76 patch 1.1.2.9, mutation serum recipes also had a chance to be dropped by the scorchbeast queen.

List
A character can be affected by these mutations:

Bugs

 * The Class Freak perk card seems to have a bug on the effects page of the Pip-Boy, where it isn't showing any reduction to the Empath and Herd Mentality negative effects while it is for the other mutations. For the Herd Mentality it seems only a visual bug, the negative effect of having SPECIAL reduced by 2 when solo and in combination of rank 3 Class Freak doesn't reduce SPECIAL at all when equip. For the Empath negative effect, this is a confirmed bug, the +33% of damage to player is not reduced at all.
 * Chameleon often glitches, and will render the character invisible from the player regardless of whether or not they're holding their weapon, wearing armor, or in motion. At times even just the character's exposed skin in rendered invisible, while their clothing remains visible.
 * The Grounded mutation with the Class Freak perk (sometimes) says energy guns do 12% less damage (the correct amount) sometimes it says 50% less damage (the standard amount) but the energy gun damage is always 50% less.
 * The Strange in Numbers perk can increase the effect of some mutations significantly. For example, combining it with the "Bird Bones" mutation can cause the player's fall speed to be reduced so much that it is possible to walk on air.
 * The Herd Mentality mutation can prevent sharing of other perk cards with the group. This appears to be fixed in the December 11th patch 1.0.3.10.