Origins of the Foulspawn

The burned remnants of a page from a book reads:
...as if humanoid flesh itself is corrupted by contact with the maddening reality of the Far Realm. How quickly this transformation takes place is unclear, but it seems to be influenced by the physical well-being of the subject, and interestingly, one's strength of will, sense of self, and grasp on reality. For this reason I caution most practitioners of the mystic arts to avoid contact with the Far Realm. It takes a remarkably healthy and centered wizard to peer into that abyss and come away unchanged. Litera..