Abominations
While a lot of people in The Wasteland would consider all Mutants to be "Abominations" those same people lack the knowledge that some of the earlier, more primitive Mutants still exist. These unstable creatures never quite left the toxic genetic miasma that spawned them and their brethren, and as such can only be found in areas of astronomical rad count (and on rare occasions forgotten underground bunkers). They are little different than the proto-mutants from the tumultuous days immediately following Skydark, and are a hideous sight to behold by mortal men. They are completely eldritch in appearance, often a shapeless shuddering mass of molten discolored flesh with countless prestigious limbs and sightless eyes. They moan, hiss, and scream from a multitude of orifices and ooze toxic sludge from every pore. Jagged bone may jut out from it's body one minute, and the next a whiplash of tendon will snap out at high speed, ensnaring anything made of biomass to subsume within itself and add to it's vile girth. They are neither mindless nor are they sentient, although in theory they might gain true sentience if enough victims of higher intellect were consumed by one of these horrors. Luckily for everyone that most creatures, human or otherwise, often can not survive more than a few seconds in such glowing hot rad pits unprotected, let alone long enough to reach one. This hazard induced isolation combined with the fact that Abominations feed off radiation much like a plant feeds off sunlight is the main reason so very few have ever had the misfortune of seeing an Abomination.