Mark of the Ninja
38 Achievements
500
10-12h
Gallows
Terrify a guard using the result of a hanging stealth kill five times.
10
How to unlock the Gallows achievement in Mark of the Ninja - Definitive Guide
lugadi
TrueAchievements
TrueAchievements
Play through the level until you get to the locked door. There will be two guards patrolling the area with more on upper levels. Dangle from the post (be careful of the sudden flashes of lightening) and wait for one of the guards to walk passed and kill him. Once the second guard sees him and gets terrified, restart from the checkpoint and do it 4 more times.
Shiftie
The first method requires the Hangman's Hymn stealth kill, which can be purchased from level 3 onward. Once you have it unlocked, sit on a grapple point and hold 
to slide down your grapple hook when you're above and enemy and press 
to finish them off.
Alternatively, you can wait until you get the Grim Harbinger Technique and simply grab a corpse and use 
to tie them to any surface you can dangle from. This cuts out the waiting on someone to walk buy your perch so you can Hangman them.
In both cases, once another guard gets close they'll freak out and start shooting the corpse (should note that it needs to be within their view range).
You can easily grind this out on the grapple points leading up the the Transformer part of Breaching the Perimeter.
