At the end of Metroid II, Samus Aran comes across a newly hatched Metroid that imprints on her and adopts her as its mother. In response, Samus defies orders to exterminate all Metroids and saves the baby. The baby went on to play a major role in Super Metroid, the end of which sees the baby sacrifice its life for Samus while fighting against the Mother Brain. https://www.youtube.com/watch?v=sWAZscxlmPw Anyone who has had a child or pet understands why this death is so sad; the baby Metroid loved Samus so much that it was willing to die for her. It demonstrats that the Metroids, the main antagonistic creatures of the games, are highly intelligent, which makes you question whether they ought to be exterminated at all. Adding new layers to the mythology of the Metroid series while personalizing Samuss connection with them, the death the baby is one of the greatest dramatic twists of the franchise.