An unfreezable Metroid (also referred to as Sector Zero Metroids or Genetic Metroids) is a mature larval Metroid that has been genetically manipulated to overcome the species' mortal vulnerability to cold, to maximise their potential as bioweapons. In the first Metroid Prime game, according to the Pirate Data, Metroid Forces, the Space Pirates wanted in the future to find a way to shield Metroids from their vulnerability to cold, but were seemingly unsuccessful, or they never tried.