There are two ways of mutation design, organ and effect. Organ is looking at what changed and is easy to use for physical and plant mutations. Effect doesn't bother with what has changed, just the mechanical benefits or penalties caused by the mutation. I use both but I prefer the former. Here are 29 mutations listed by the organ (or tissue) that has mutated.
Tails
Bungie Tail
The mutant's tail can extend and contract without harming the mutant. The distance is 1' per point of constitution. 50% of these tails have grasping spines and the rest can curl and grasp.
Hooded Tail
The mutant's tail has flaps of skin that can be extended, like a cobra's hood. If the mutant is awake when falling and extends the hood, falling damage is cut in half.
Hooded Tail, False Face
The mutant's tail has flaps of skin that can be extended, like a cobra's hood. With this mutation, when the hood is extended, the end of the tail looks remarkably like the mutant's head. It has a poor armor class (8) but damage is healed twice as fast.
Hooded Tail, Patterned
The mutant's tail has flaps of skin that can be extended, like a cobra's hood. When extended, one side of the hood starts to glow slightly and show weird color patterns (50/50 front/back). Every creature that looks at the hood and is within 30' of the mutant must save versus stun or be confused for as long as they see the hood plus d4 rounds.
Hooded Tail, Spring Launch
The mutant's tail has flaps of skin that can be extended, like a cobra's hood. When the hood is extended, the tail can be used to jump. The distance for a vertical jump is 2' per point of strength and a horizontal jump is 5' per point of strength.
Tusks
Head Shield
The mutant's tusks are large and cover most of the head. The mutant is treated as if wearing a helmet at all times, as a -1 bonus to their armor class and have no peripheral vision (suprises on a 1-5 on a d6). Any tusk attacks is lost.
Staw Tusks
The mutant has enlarged upper tusks (i.e. they point down) that are hollow. They allow the mutant to drink without bending or lowering their head. This makes suprising the mutant much more difficult while they are drinking (only 1 on a d6).
Brittle Tusks
The mutant's tusks are constantly growing and shatter with ease. Six times per day the mutant can break a tusk and create d6+4 caltops. These do not make good ranged weapons, except as sling ammo, but can be used as normal caltrops otherwise.
Hooves
Padded Hooves
The mutant has wide, well padded hooves that allow it to run on snow or mud without sinking. This only works as long as the mutant is running. When they stop, they sink.
Leg Shields
The mutant's hooves have grown upwards, encasing the lower leg. The mutant has damage resistance 5 against physical attacks towards the protected areas.
Shifting Hooves
The mutant's hooves can transform into fingers, tentacles or other short digits to allow manipulation of objects. They are just as useful as human fingers (though animals like horses will still have trouble bending their legs in a similar manner to human arms).
Eyes
Retract and Replace Eyes
The mutant's eyes can be quickly withdrawn into the head, making them immune to blinding attacks. The space left behind is filled with another organ. It might be a tentacle, poison spewer (range 5'), horn made of goo or whatever the player can imagine (with ML okay). When the organ is retracted, the eyes surface and the mutant can see again. Both eyes are affected at the same time.
Multipupiled Eyes
The mutant has d3+1 pupils. Each one can see a different part of the electromagnetic spectrum. One is always visual light and the others may be radio, microwave, infrared, ultraviolet, x ray or gamma radiation. There is a 1% chance that the mutant has see alien energy through one set of pupils (see Wisdom from the Wastelands #7). The mutant can only use one set of pupils at the same time.
Muscles
All Gristle
The mutant's muscle tissue is gristle. Predators will try to eat the mutant last, but only after one successful bite attack. The toughness of the tissue gives the mutant +1 to strength and -1 to armor class.
Flowing Muscles
The mutant can move muscle tissue around their body, providing several benefits. It can alter the mutant's outline, confusing some computer sensors. It makes the use of restraints such as ropes and cuffs against the mutant useless. Arm and leg strength can be modified. For a reduction of movement, the mutant's damage increases and reverse. 30' (10') of movement is equal to 2 points of strength.
Digits (Fingers/Toes/Tentacles/etc.)
Tool Digits
The mutant can alter one kind of digit into some useful tool. This is a minor morphing effect that may include bone, skin and muscle. The mutant has a +10% bonus to technology rolls for lower tech artifacts and crafting.
Sensory Digit
The mutant has sensory organs in one kind of digit. It may be weak eyes (light/dark), ear drums, odor detecting cells, etc. These organs are not vulnerable to attacks on their sense because they are not fully developed organs.
Second Set of Toes or Fingers
The mutant has a set of toes or fingers that emerge from the wrist. Mutants that have hands can drop to all fours and double their movement rate. Mutants without hands now have fingers and can manipulate objects as if they had hands.
Joints
Moulting Segment
The mutant can drop a segment of limb and regenerate it. For every segment lost (digits/tail, hands/feet, forearms/lower legs, upper arms/upper legs), the mutant takes one week to regenerate the lost parts.
Reversable Joints
This is much more than double jointed. This mutation allows all of the mutant's joints to be used in 360 degrees, making them much more limber. They have + 30' (10') to their movement rate, +2 dexterity plus any bonus the ML can think of in the situation.
Scales and Spines
Shifting Scales or Spines
The mutant's scales' or spines' shape can be altered with a thought. They can be sharp, inflicting d4 points of damage to everyone and thing in contact with the mutant. They can be smooth as glass, making it easier to get out of ropes and similar restraints. They can migrate on the body, healing one point of damage per round (max 5 per day). They can be hooked, thus allowing the mutant to climb most surfaces without a threat of falling. And they can interlock, putting a penalty to armor class (+2) in exchange for damage resistance 3.
Chrysalis Scales
The mutant can merge their scales, forming a chrysalis. The mutant must remain within it for at least 24 hours and can remain for as long as the mutant can survive without food (so a month or so for mutant humans). Each day the mutant heals 10 points of damage. For each week, the mutant regenerates a lost limb or other major part. For those who go a whole month, they can gain one ML approved mutation. This mutation is replaced every time the mutant goes through the chrysalis change.
Needles/Leaves (note that only 50 can be shed per day)
Plants have their own versions of Chrysalis Scales, Leg Shields and Brittle Tusks.
Match Needles/Leaves
The mutant can drop needles or leaves. After one minute the dropped part becomes highly flammable. 10% of mutants have a version that ignites automatically after the minute.
Steel Needles
The mutant can drop needles or leaves. After one minute the dropped part gains the strength of steel and remains so for several years. They can be used as blowgun ammo, lock picks, various tools and "wrenches" used to damage machines. Steel needles used against a basic android or robot do either double damage (as ammo) or d3 points (if used by hand).
Reactive Needles
The mutant can drop needles or leaves. When placed in a specific liquid, usually water, alcohol or blood, the needle reacts and turns the liquid into something else over one turn. This is a plant version of the Chemical Gland mutation.
Floating Needles
The mutant can drop needles or leaves. After one minute, the parts become lighter than air. The Elder People created this mutation to replace the failing helium supply. Plants with this mutation usually collect the needles/leaves in containers and use them to make balloon cranes or airships. It takes a month of needles/leaves to lift 10 pounds.
Fleshy Needles
The mutant can drop needles or leaves. After one round the parts turn into animal flesh. After an hour the flesh dies and starts to decay, making a noxious odor that make cause nausia in animals (including humans). A save versus poison is needed. Failure results in d4+2 rounds of retching.
Light Sponge Needles
The mutant can drop needles or leaves. After one round, the part absorbs all light within 5'. After an hour of this, the part combusts, creating a flash of light equal to the Bright Eyes mutation.
Holographic Needles
The mutant can drop needles or leaves. After one minute, the part projects a small hologram. These are memories or fantasies from the imagination. None can be used offensively but they can distract (enemies within 30' of the part must save versus stun or be distracted and lose their initiative the next round). For some plants, this is their only form of communication with non-plants.