|The following is based on Fallout Shelter or Fallout Shelter Online and some details might contradict canon.|
The player's dwellers are sent to a randomized location in order to rescue a potential pet. Feral ghouls, including a glowing one, are the predominant threat, although radroaches may also spawn. The top floor always has a glowing one accompanied by four more ghouls. Upon its defeat, the glowing one's corpse yields a pet carrier as a reward.