The nemesis system is an special thing in the game Shadow of Mordor created by Monolith.

What is going on with the nemesis system if you die?

Well if you die as tailon you are going into the mind of the uruk that killed you. What you sees there is wonderful the uruk that killed you for example a random uruk in the army of sauron (not a captain or a warchief) then you see that he gets a name for example torcha the cowward if he kills you again he is gonna be a captain and then elite and then warchief enz. if you kill him then he is gone and someone else takes his place nemesis system