• Your best bet to get this achievement is on the "Survival of the fittest (extreme)" challenge map round 3, because it will have enough enemies to do the perfect combo and it doesn't have any annoyances (like a Titan henchman).
  
• Use redirect (jumping over enemies) many times, as it can save your combo, you can position yourself for takedowns and it gives you time to plan your next move.

• Punch (LMB)
  
• Counter (RMB)
  
• Evade and Redirect (Space)
  
• Stun (MMB)
  
• Beatdown finisher (Stun + LMB mashing)
  
• Aerial attack (Stun + Space)
  
• Ultra stun (MMB x3)
  
• Combo batarang ('1' key x2 !when combo meter flashes yellow!)
  
• Instant takedown (E)
  
• Batswarm (R)
  
• Multiple ground takedown (T)
  
• Disarm and destroy (Y)
  
• Ground takedown (Ctrl + RMB)

Now I will describe the order which suited me the best and I think is the easiest. First of all, you will need to divide the moves into 3 phases:

• First Phase: do the most basic ones first (Punch, Counter, Stun, Redirect (also jump to an open area (counts as Evade move) and be careful not to do an Aerial Attack))
  
  
• Second Phase: now you will need to do the takedown moves 1 by 1 (E, R, T, Y) and the Combo batarang (remember: it only counts when the combo meter is flashing yellow). Just keep punching and redirecting to safely gather the yellow combat indicator between the moves.
  
  
• Third Phase: not much enemies left and that's good for us, because now comes the interruptable moves. By this point you should have at least 3 enemies still fighting, if not.. then you might not make it. What you want to do now is carefully execute the Aerial attack, then KO all of them except 2 guys. Redirect one of them then quickly Ultra stun the other one (this should render the guy stunned on the ground for a long time) and then use the Beatdown finisher on the previously redirected guy... and then finally Ground takedown the Ultra stunned last guy (jump near him first just in case and BE CAREFUL not to push one of them to the electric fence!).

You might not make it on the first try.. no worries, I practiced a lot until I got it right myself^^
Good luck and thanks for reading!