For this achievement you must complete the Predator Challenge "Batcave" using only Beat Downs (
then
repeatedly)
AND without taking any damage. If your health bar appears on the screen, start over.
The most convenient way I found to do this challenge is using a little trick: when approaching a thug from behind, don't go all silent, run! It'll make him scared. As soon as he bows covering his head, start the beat down. Using this technique, NO ONE will go after you right away, they will only get alerted when they see the body or when the Arkham Knight tells them someone is out. If you approach the thug silently and use the beat down, all the enemies will imeddiately go to your location.
(Note: use this technique only when a thug is alone)
This achievement requires patience, because you will need to let the thugs scatter everytime they find a corpse. Be very careful of who you engage, because there are 3 thugs with camouflage, so you won't be seeing them in Detective Mode.