Ygdar Orus Li Ox

 is a colorless mutation which saves the player from death once. It can only be acquired from Guillain after leaving the Prisoners' Quarters and will be subsequently locked, if not chosen then. After it activates, it will not be possible to reset its mutation slot. If the heart icon is red, the mutation is active while a rotten heart icon means that it was used. First use unlocks the achievement YOLO! Or not?

Trivia

 * The name of this mutation, as well as its internal name, is a reference to the word YOLO, meaning "You Only Live Once".