Legs off, fins on, stick a little pipe through the back of its neck so it can breathe, bit of gold paint, make good … Monty Python

I’ve been a fan of Gamma World in most of its incarnation since the beginning. Something about it, played straight or completely wahoo, has brought me back time and again. I think it’s the Yexils.

C’mon, look at that guy, don’t you just want to feed him a puffer jacket? (Yexils eat clothing, work with me here)

The Alternity version (5th edition) was a little conflicted. The world presented was more serious, and perhaps in that vein there were no rules for mutant animals or plants as player characters. The mutant animals returned in a Dragon Magazine article, and the mutant plants got redemption from Neil Spicer. Robots however, of them there was nary a peep. It was Gamma World, but with the wahoo filed off.
One of the early ideas/hopes with Alternity was that the species in the corebook would be incorporated into the various settings that were produced. That they would become ubiquitous like dwarves and elves. In the Dark Matter setting they showed up, but having that setting set in the here and now, having them as character options wasn’t really…an option. Alternity Gamma World had Weren/sasquatch and Mechalus/androids, but I feel they missed the boat by not bringing the other Alternity species on board. T’sa and Sesheyans fit in Mechanically as written in the Player’s Handbook. The fraal can work as written if you are willing to include psionics as skills in your setting, or as mutants with Contact, Size Change: smaller, Enhanced Mental Ability: intelligence, Physical Change: major, and throw in Telepathic Blast to round them up nicely. Use them as genetically modified scientists from a long-sealed bunker and there you go. Sesheyans as mutant amphibians(?) with wings, and T’sa as little desert dwelling velociraptor wannabees with spears instead of rear talons. Give each a culture in your setting and you are off.

One good use of Gamma World is to provide abilities for alien player character species. Here are a handful of mutants and alien races made with GW mutations:

StarDrive Mutants
Shock Trooper – Hyper Metabolism; Improved Reflexes; Redundant Vital Organs; Reduced WIL – moderate; Physical Change – minor.
Vacuum Mutant – Environmental Adaptation – thin air; Radiation Tolerance; Oversized Arms; Oversized Legs; Increased Balance; Size Change – smaller; Environmental Sensitivity – high gravity – slight; Physical Change – minor; Sound Sensitivity.
Hi-G Mutants – Environmental Adaptation – heavy gravity; Improved Con; Hyper Str, Dermal Armor, Physical Change – minor; Weak Metabolism – moderate.
WarLions – Redundant Vital Organs; Enhanced STR; Night Vision; Natural Attack – claws; Physical Change – minor; Reduced INT – slight, Reduced WIL – slight.

Fading Suns Mutants
Metronym – Metamorphosis; Pheromones; Photographic Memory, Translation, Telepathic Scan; Vascular Control; Physical Change – minor, Temporary Weakness – moderate.
Mentat – Natural Learner; Photographic Memory, Hyper INT; Quick Thinking; Weak Metabolism – extreme.

Traveller Mutants
Aslan – Natural Attack – improved; Night Vision; Increased Speed; Improved Senses; Physical Change – minor; Reduced WIL – slight; Light Sensitivity.
Vargr – Natural Attack; Enhanced Senses; Increased Speed; Life Detection; Psychic Perception; Reduced WIL – slight; Physical Change – minor, Reduced INT – slight.
Zhodani – Pheromones; Enhanced PER: Enhanced INT; Natural Learner; Photographic Memory; Radiation Sensitivity; Thermal Intolerance; Severe Phobia. (Possibly Attraction Odor?)
Kafer – Redundant Vital Organs; Dermal Plating; Radiation Tolerance; Physical Change – major

XXVc Mutants
Asterminer – Dependency – Zero-G environment, Dermal Armor, Ordinary Vacuum resistance, Physical Change – major
Belter – Dependency – light Gravity, Quadro Dexterity, Duality
Cadrite – Thermal Tolerance, Empathic Symbiosis, Skeletal Enhancement, Dependency- hive mind
Delph – Dependency – water, ordinary Enhanced respiration, Cold resistant, Major Physical change
Depthine – Gills, Amazing environmental sensitivity – low pressure, Major Physical change
Desert Runner – Reduced PER, Suscept to heat, Adapt to cold, Enhanced Senses, Suscept to high pressure
Desert Runner II – as DR I, + Natural attack, Obsession 6: Protect pack
Devastator – Light Susceptibility, Color Blind, Night Vision, Armor Plating, Adrenal Control
Europan – Sensitivity to light, Resistant to temperature extremes, Night vision,
Ganyman – Immunity to cold, gills, Extreme dependency –water, Enhanced senses – underwater, Slick skin, Physical Change – major
Lowlander – Resistant- heat, toxins, Night Vision, Increased STR, Reduced PER, Physical Change – major, Armor Plating
Lunarian – Resistance – radiation, Night Vision, Sensitivity – light, Reduction – STR, Enhanced INT, Adaptation – light gravity
Martian – Enhanced PER, Environmental Susceptibility – heavy gravity, Enhanced Senses Adaptation – light gravity
Mercurian – Resistance – heat and radiation, Environmental Sensitivity – cold
Ringer – cybernetics
Sharc – Dependency- salt water, Gills, Dermal Armor, Natural Attack, Physical Change – major
Sidhe – Dependency – light gravity, Telekinesis, Amazing INT, Amazing WIL, Reduced STR, CON
Spacer – Symbiotic respiration, Dermal Reinforcement, Photosynthetic Skin, Physical Change – major
Stormrider – Reduced DEX, Reduced PER, Radio Sense, Toxin Tolerance, Wings, Size Change (x2), Physical Change – major
Talan – Enhanced Senses, 0-G training, Duality, Enhanced Dex, Reduced PER, Physical Change – major
Terran – no change
Terrine – Natural Attack, Dermal Armor, Reduced INT, Reduced PER, Aggression, Major Physical change
Tinker -Size Change – small, Night Vision, Increased DEX,
Venusian – Toxin Tolerance, Environmental Adaptation – heat, high pressure
Worker – Extreme WIL reduction, Amazing STR increase, Good CON increase, Dependency – food supplement, Fade Out

Some notes: Dependency you need to make a CON Feat check to avoid losing 1 fatigue point per day without the substance.