Fallout 76 mutations

Mutations are a gameplay mechanic in Fallout 76, which are acquired by the player character when exposed to radiation. Mutations provide both a positive and negative effect, similar in function to traits in other games in the series.

Characteristics
Mutations are semi-permanent effects that provide both positive and negative effects. Whenever a player takes Radiation damage, they have a chance to gain a mutation, equivalent to 5% per 5 points of radiation damage. This can occur from being struck by excessive background radiation from a source such as zones devastated by nukes, irradiated creatures, radioactive waste, etc. Players cannot acquire a mutation from radiation until level 5. If a mutation is acquired from radiation damage, another mutation cannot be acquired until the player leaves that server.

It is possible to acquire up to 18 of the 19 available mutations at the same time. The exceptions are Carnivore and Herbivore, which prevent one another from being acquired.

The Class Freak perk will reduce the negative effects of a mutation by 25/50/75%, while Strange in Numbers will grant a 25% increase to the positive effect if teammates are also mutated. Mutant's legendary items will only activate if the player character is mutated.

Serums
By consuming a mutation serum, the corresponding mutation will be applied to the player character and its negative effects will be nullified for 1 hour. If the player already has that mutation, then the negative effects of the mutation will be suppressed.

Serums and their recipes are sold only by the MODUS science terminal in the Science Wing of the Whitespring bunker.

Removal and prevention
Every time the player uses RadAway, RadAway: diluted or a decontamination shower, there is a chance that a randomly selected mutation will be removed. They can keep using RadAway for more attempts to remove a mutation. Mutations cannot be removed through death. However, a percentage of rads is removed upon death. Nuka-Grape, brahmin milk, or the perk cards Healing Hands, Rad Sponge and What Rads? can also be used to remove rads without risk of curing mutations.

The Starched Genes perk allows for locking mutations, as it reduces/eliminates both the chance of becoming mutated and their removal chance. Radiation protection gear (e.g. hazmat suit) reduces the chance of mutation.

Suppression
Even with the Starched Genes perk, the positive effects of current mutations can be suppressed by Rad-X for 10 minutes. To avoid the suppression effects of Rad-X, the diluted version or RadShield can be used to gain Radiation Resistance. If the player character already has a mutation, the respective serum will suppress the negative effects of the mutation for 60 minutes. For example, consuming a marsupial serum while already having the Marsupial mutation will temporarily remove the Intelligence debuff.

Mutations list
A player character can be affected by the following mutations:

Bugs

 * Prior to Fallout 76 patch 1.0.4.13, the Strange in Numbers perk could increase the effect of some mutations excessively. 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.
 * Prior to patch 1.0.3.10, which fixed the issue, the Herd Mentality mutation could prevent the sharing of other perk cards with the group.
 * Prior to patch 1.1.4.3, which fixed the issue, the Class Freak perk card had a bug on the effects page of the Pip-Boy, where it would not show any reduction to the Empath and Herd Mentality negative effects while it is for the other mutations. For Herd Mentality, it seemed to only be a visual bug, as the negative effect of having SPECIAL reduced by 2 when solo and in a combination of rank 3 Class Freak did not reduce SPECIAL at all when equipped. For the Empath negative effect, this was a confirmed bug, as the +33% of damage was not reduced at all.
 * Prior to patch 1.1.4.3, which fixed the issue, the Grounded mutation with the Class Freak perk (sometimes) said energy guns do 12% less damage (the correct amount)m sometimes it said 50% less damage (the standard amount) but the energy gun damage is always 50% less.
 * Prior to patch 1.2.2.9, which fixed the issue, Chameleon often glitched, and would render the character invisible from the player regardless of whether or not they were holding their weapon, wearing armor, or in motion. At times even just the character's exposed skin was rendered invisible, while their clothing remained visible.

Behind the scenes
Mutations were originally planned to have a cosmetic impact on the player, changing their appearance temporarily or permanently.