This achievement is rewarded for viewing the secret Easter Egg ending to the game on Carpathian Mountains'
Upon reaching the end of the train and talking to Arthur Edwards, you'll be given a Serum to take him out. You can also use your weapon, and other objects on the train. Instead, wait 47 seconds, and a new option will appear where you can inject yourself. Do this and unlock the "A New Father" redacted challenge, this achievement, as well as a very cool original Hitman easter egg.