Fallout 76 mutations

Mutations are a gameplay mechanic in Fallout 76, where exposure to radiation has implications on the player character. It is not exclusively tied to limiting SPECIAL stats or max health, it also allows the player character to develop various mutations, which act like traits in other games in the series

Characteristics
Mutations are a type of condition that give a mixture of powerful positive and negative effects. Whenever one takes Radiation damage, they have a chance to gain a Mutation, equivalent to 5% per 5 points of radiation damage (if they are not below level 5). This can occur from being struck by excessive background radiation from a source such as zones devastated by nukes, irradiated creatures, radioactive waste, etc. It is possible to acquire up to 18 of the 19 available mutations at the same time. The sole exception is Carnivore and Herbivore, which prevent one another from being acquired.

The Class Freak perk will reduce the negative effects of a mutation by up to 75%, while Strange in Numbers will grant a 25% increase to the positive effect if teammates are also mutated. A player character wielding a legendary weapon with the Mutant prefix will do 10% more damage when mutated.

Mutations may also be gained by consuming a mutation serum which allows a specific mutation to be gained. Serums are consumable items that will grant a specific Mutation as one uses it, and temporarily suppresses the negative effects of the Mutation.
 * Serums

All serums and their recipes are sold by the MODUS science terminal at the Whitespring bunker Science Wing terminal. Recipes for the serums can also be purchased from MODUS but have a steep base price of 23000 caps each, but with the Hard Bargain Perk card and higher Charisma levels, the price can be reduced. Prior to patch 1.1.2.9, mutation serum recipes also had a chance to be dropped by the scorchbeast queen.

Prevention and removal
Mutations are semi-permanent. Every time the player character uses RadAway or a decontamination shower, there is a chance that a Mutation will be removed. They can keep using RadAway for more attempts to remove a Mutation. Radiation protection gear (e.g. hazmat suit) reduces the chance of mutation.

The Starched Genes perk allows for locking mutations, as it reduces/eliminates both the chance of becoming mutated and their removal chance. Mutations cannot be removed through death. However, a percentage of rads is removed through each death, so it's possible to mostly but not completely decontaminate oneself through multiple deaths if Starched Genes is not yet acquired. Nuka-Grape, brahmin milk, or the legendary perk card What Rads? can also be used to remove rads without risk of curing mutations.

Suppression
Even with the Starched Genes perk, a Mutation's effects can be suppressed for a time with the use Rad-X. The suppression lasts for 10 minutes. To avoid the suppression effects of Rad-X, the diluted version or RadShield can be used. If one 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 remove the intelligence debuff.

Mutations list
A player 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 a combination of rank 3 Class Freak doesn't reduce SPECIAL at all when equipped. For the Empath negative effect, this is a confirmed bug, the +33% of damage is not reduced at all.This appears to be fixed in the May 7 2019 patch.
 * 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 is rendered invisible, while their clothing remains visible.This appears to be fixed in the August 20 2019th patch.
 * 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.This appears to be fixed in the May 7 2019th patch.
 * 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 the sharing of other perk cards with the group. This appears to be fixed in the December 11 2018th patch 1.0.3.10.