From Introduction:
The wastelands that comprise the Twisted Earth of DARWIN'S WORLD are home to myriad of horrendously-mutated beings, from intelligent character-types worthy of interaction to simply the cannibalistic or predatory creatures that prey on the weak or solitary. Dangers other than the ever-present radiation and the chemically contaminated ecosystem do exist out there, and are rightly feared by all folk of sound mind.
This sourcebook, the Terrors of the Twisted Earth, is only meant to give a mere sampling of the kind of mutated beasts that pose threats to player characters in DARWIN'S WORLD. A description is given of each infamous creature, along with game statistics so that they may be pitted against characters if the referee so wishes.