In the deep wet dark dwell the Memnophage, the eaters of memory. These twisted, serpent like creatures are neither demon nor beast, but an unholy mixture of the two. They travel in schools along the bottom of the Styx, plucking away the stray traveler who chances to travel too close. Memnophages have been known to attack demon and soul alike, and as such are usually periodically exterminated to keep their populations low.
He who is taken victim is left alive, but is drained of all knowledge of everything, even the knowledge of how to walk and speak. A soul left in such a state will find himself in dire straights indeed.