How do you do a takedown after a smoke pellet?

One of the challenges in Batman: Arkham City is

Use the Smoke Pellet to disorientate an armed enemy and follow up with a Takedown

But how exactly do you do this? Every guide I've found just says something along the lines of find an armed enemy, throw a smoke pellet at them, then do a takedown. But there is never any takedown option. I've tried just punching them, standing in front of them, standing behind them, crouching, and there's never a takedown prompt. They just stand there flailing about a little until the smoke clears.

So what exactly are the inputs required to complete this challenge?

1 Answer

Probably the easiest method is the Line Launcher Takedown.

After disorienting an unaware enemy from a distance (6, right-hold, left-click), fire the line launcher (8, right-hold, left-click) at them, then right-click on approach.

A Special Combo Instant Takedown (E) may also be possible, but you need a group large enough to build combo but with few enough guns that you don't just get shot. There will be a small window to drop the pellet and target the correct enemy in-between combo moves.