Hunchback: Causes the subject to have a deformed, hunched over back. Slows movement speed and decreases social abilities.

Dronelike: Subjects mental capabilities have regressed. They are more basic and feral but strangely are very obedient. Slightly increased melee damage, reduced mental break threshold, heavily reduced social abilities. Can no longer perform research.

Regeneration: Subject can regenerate wounds at surprising speed. Bleeding will stop on its own much faster than in normal people and wounds will heal much faster. This also means they can take a bit more of a beating before being downed/killed. Downside is that they need food more often to make up for the lost energy in regeneration (maybe a lot more). Possibly make it so that entire lost limbs will eventually grow back but it takes a long, long time. Perhaps as a balance when the limb/bodypart grows back it has scars from imperfect regeneration. I dunno.

Nerve Degredation: Subjects nerves have essentially withered and died. They are much less sensitive to pain, you could riddle them with bullets and it wouldnt increase their pain much, in exchange they are constantly in moderate pain. Decreasing their mood.

Nightvision: Subjects eyes have become like that of a cat or other animal with natural nightvision. This boosts their sight and makes it so that they dont mind the dark. However others tend to find it weird and it subtly repels them in social interactions.

Progeria: Causes the subject to begin experiencing extremely rapid aging. This causes them to suffer from age related health problems early.

Digitigrade: Subject has experienced reformation of their bone structure resulting in their legs being reshapen. They move faster but have slightly reduced carrying capacity.

Sanguismutatio: This mutation results in the subjects immune system failing. They struggle to build up immunity to diseases without lots of medical aid. However bleeding stops on its own quickly and the subject is highly resistant to bleeding out.

Duocordibus: Based off of a genetic modification from Xcom, subject has grown a second heart. This makes it so that what would have been a lethal blow is more likely to just down them. They take a bit longer to bleed out.

Sixth Sense: Very rare mutation, it's unknown exactly what happened to the subject but they appear to have grown another sensory organ inside of their body. This sensory organ is unlike anything your doctors have seen. They seem to have heightened reaction times and can somehow tell something is coming before it happens. However they are rather distant and dont act much like themselves anymore, they claim that they can 'see' things that no one else can. Exactly what these 'things' are is unknown and perhaps that is for the best.

Personally I would love to see some of the skin related mutations changing the appearance of the character. I know hair can go gray for example, I would love to see a human who took the drug possibly become blue, green, red, etc. It would be especially striking in games without alien races (although I play with most of them).

As for mutations I've got a few in mind, I'll dive in once there is an updated list as to not be too redundant.

I think you should add alot of real world mutations like parkinsons and wolfman syndrome so it has a bit more realism but also add something like increased strength and speed to even it out so that there isn't just down sides.

@Eastwardrope
I thought to avoid real world mutations because most I could find were more genetic defects than mutations. Really not providing any benefit and more just making the persons life hell. I thought about a wolfman syndrome type thing too but theres already a 'fur' mutation so I kinda assumed its basically the same idea. Maybe instead theres a literal wolfman mutation, like lycanthropy, maybe like once every season the person goes into a berserk rage for one entire night but also has enhanced speed and melee damage for that one night. That may be hard to program though.

Drug resistant: Drugs simply don't affect them as much. They have -50% chance of addiction, and recover from withdrawal 50% faster, but drugs only last half their normal duration.

Alcohol resistant: Same as above, but with alcohol.

X-ray vision: They can see weak points and shoot more easily at them (+20.00% shooting accuracy), but are constantly distracted by it (+10.00% shooting time).

Stabilized arm: They handle recoil far better on automatic weapons (+15.00 shooting accuracy with auto or burst fire weapons).