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In Batman Arkham Origins (and AC incidentally), if I try to grapple onto a ledge from below (in order to silent-kill a guard), about half the time I'll hang from the ledge and the other half of the time I'll end up automatically climbing up, and therefore exposing myself to the guards.
Is there a way to grapple onto a ledge without climbing all the way up (i.e. hang from the ledge), so I can perform a ledge takedown?
The Inverted Ledge Takedown requires you to stand on a ledge such as a guardrail. Once you have an enemy approaching below you, and you're given the Takedown prompt, wait a few seconds for the enemy to be facing the opposite direction. (i.e.: If you're facing away from the wall, wait until your target is facing the wall) This YouTube video posted in another answer shows exactly how it's done (It should start just a few seconds before the takedown). Basically, the bat is facing the opposite direction of the target when he performs the takedown.
Here's a picture showing the actual takedown (to avoid link rot):
By default:
I played on the Xbox 360, so I'm not 100% on the controls for the PC. If someone makes a correction in the comments, I will edit it into the answer to correct the controls.
You unlock it by doing one of the game's side missions. Really stupid they don't show you what can be unlocked, I found out about every single move in the game before this one.
You have to do Bird's side missions to do it. I've no idea who Bird is or what the side missions are like- but it's those ones we need to do.
Took me like a further two hours of playing (already at about 10-11 hours) before I saw this.
Hopefully this'll be useful to someone in the future.
Best Answer
In Arkham City at least, this is accomplished by holding RB (or the F key if you're using keyboard) instead of tapping it.