He's always hungry
An amorphous blob of gelid flesh covered with eyes and mouths.
“One would do well to avoid the grasp of the moat-creature. Bob’s always hungry.” – Bandren
This creature, whom many say was once a Man (although Sargan is no longer around to confirm or deny this), was placed in the moat around the White Tower many years ago. It is bound to the Tower, and remains lurking within the moat due to powerful magics that keep it there.