Okay Gamma World proper is Earth but that is too far removed for me... so I decided to list Gamma III (in the Gamma System, once called Nova Terra) as home world for many critters, but some creatures I am going to give them an alternate SF origin if something strikes me as fitting well. As Gamma III is a UPF colony gone to hell in a hand basket the alternate homeworlds will still work as those creatures could have been introduced to Gamma III before it's apocalyptic event. Blue Plague was just one of many bad things that happened there, as the plague spread other disasters occurred including but not limited to laboratory research facilities having breaches as no workers where maintaining systems and then either automated systems going into kill the inhabitants of area to contain the contamination or the lab experiments escaped, other facilities such as power plants unmanned began having problems till melt down occurred, areas of the planet that where off limits and patrolled since the Sathar's last attack (mostly because they where dangerous for one reason or another) where left unguarded & unstudied so creatures could wander in and out at will, City Mayors became desperate ordering people mass killed (to stop diseases, or prevent the whole city from starving, to maintain power, to purge down to one race and so on) new & old illnesses not seen for centuries reemerged into new plagues as medical care, safe food/water supplies became scarce, and sanitary conditions plunged into filth. In the end chemical toxins, radiation, plagues, poisons, mutations, sathar mutagens, barbarism born out of the need to survive, fear, hate and other stresses on the colony finally collapsed it into primitive conditions and creating a GW setting. All 4 races where present on Gamma III when this happened, but Gamma III was originally a Human Colony so they where still the dominate group at the time.