This is a highly variable mutation, and can be used to create any number of body weaknesses. Examples include brittle bones or susceptibility to bruising. These would increase damage by falls or other blunt force trauma by a degree decided on by the ML. However, damage should usually be increased no more than by +3 per die of damage.
Other forms of physical frailty includes:
Epidermal Susceptibility: The epidermis of the mutant becomes defective in some way, either causing 1d6 hp of damage for coming into contact with usually harmless substances (such as water), or adding +1 per die of damage caused by specific injury, such as by fire, radiation, slashing weapons, or penetrating weapons.
The mutation can also be something that constantly creates a serious inconvenience for the character, such as glowing skin, uncontrollable pigment shifting, or skin that always attracts certain kinds of vermin or larger creatures.
Hemophilia: The mutant’s white blood cells are diminished in count, preventing him from healing as quickly as a normal specimen of his kind. This mutant may only heal 1d3 hp every other day. Once the character is injured, he begins to bleed profusely, losing 2 hit points per round until the wounds can be properly bandaged.
Pain Insensitivity: The character lacks the awareness that living creatures normally possess with regard to their bodies and immediate surroundings. The character does not feel pain when injured, even if a weapon has penetrated his body. The character will not be able to tell how much damage he has sustained without making a visual checkup of his entire body. The ML should keep track of the character’s hit points.
Pain Sensitivity: The character’s nervous system is very susceptible to injury, resulting in all damage to the character being doubled.
Poison Susceptibility: This mutation makes all poisons much more dangerous to the character. All saving throws versus poison are made with a penalty of -4.
Reduced Immune System: Whenever the character falls ill, whether it is from infection caused by combat/misadventure, or airborne infectious diseases, the character suffers an extra 10 hp of damage per day. If using the optional Disease rules characters with this mutation suffer a -4 saving throw adjustment against diseases, and the duration is doubled.
Reduced Oxygen Efficiency: This mutation makes it harder for the character to get oxygen into the circulatory system. This means that, after any amount of extended physical activity (including combat) lasting more than 5 rounds, the character must rest or fall unconscious for 3d6 rounds. Further, when exploring ruins these characters need to rest for 1 turn after 3 turns of exploration.