Feral ghouls are creatures that appear in Fallout Shelter.
The degeneration into a feral state (referred to as ferocious post-necrotic dystrophy) is not fully understood. It is known that it is a result of a degeneration of the brain (which is not affected by the regenerative mutation of the spinal cord) and emerges following the atrophy of higher brain functions, accompanied by an increased level of aggression and appetite. When the loss of capacity for thought is complete, a ghoul is considered feral. The factors that may cause a ghoul to enter this state are unclear, but anti-social or isolated ghouls are more susceptible to it. Exposure to intense radiation may also be a factor – feral ghouls have no body heat and emit lethal levels of radiation, indicating that feral ghouls are for all intents and purposes dead, their functions sustained only by their high irradiation. This allows them to survive for centuries, relying only on the energy provided by radiation – at the expense of a horrifying, emaciated appearance. Understandably, the process is irreversible.
Feral ghouls can attack the player's vault during random events, or can be encountered in certain quest rooms as an enemy type.