Hello everybody!, I speak Portuguese and I'm typing through google translator, I hope you understand any grammar error.
To unlock this achievement is simple and easy, follow these steps:
I chose chapter 5 as did the two achievements Finish him Shadow! and Shhhhh! LEVEL OFFICER it has many enemies.
Did all silents kills with Shadow and then I walked through the stage calmly, if die no load the checkpoint let the game do it for you because the kills made will be accumulated.
Fight unarmed with the weaker enemies, take at most 4 strokes with B grab him throw down the Shadow send finish him, it's called combo kill to get a new combo kill defending and wait 12 to 15 seconds for Shadow is available again.
I made around 30 combos went to the end of the level and 2 achievements unlocked!
Thanks and have helped yours!