The Rhaumbusun is a very dangerous monster if one lacks free action. They have the ability to use a gaze attack that will paralyze for d4 turns if you do not possess free action. Reflection does not protect against the gaze, but blindness will. Fortunately, their low level and high AC mean that they are very easy to kill once the paralysis can be negated. They can only be generated in Gehennom, by which time their unusually low difficulty will likely result in them never being randomly generated. They can be created by summon nasties. There is always a rhaumbusun named Izzy in the black market that will turn hostile if you attack One-eyed Sam.