To earn the trophy that's called "Death and Glory", you must take out at least twenty thugs by employing Fear takedowns.
You can earn this throughout your first play through of the game. Basically, you will be in various predator encounters that involved at least up to ten, if not more, thugs that are patrolling around the area.
If you can take out one guy with a knockout smash, it's definitely going to attract attention from the other thugs. Make sure to stay out of sight and wait for them to surround the fallen guard. If you happen to be near them and the prompt says for you to do a Fear takedown, go ahead and do it. Depending on how much you've invested in your skill tree, you can take out at least up to five guys. If not, just do it little by little.
Once a Fear takedown is complete, quickly get out of sight and find a guard that's isolated from the others, then use a Silent takedown on him to re-charge your Fear takedown.
Rinse, wash, and repeat until you've taken out twenty guys throughout your play through and your Trophy should unlock.
Have fun and good luck!