Cape Counter can be done with
and you will want to do this as an opponent attacks to Counter/Parry them. You can also add Batman's Meter Burn
at the end of Cape Counter with the Advanced Parry ability. You get abilities automatically when you level to 10 and 20 or from Motherboxes. I can confirm however the achievement can unlock with the AI. I had it unlock during the Multiplayer AI Battle Simulator.
I was unable to do this in 2 player mode with a second controller successfully as it requires some type of attack to prompt and couldn't get the timing right solo. I also did not try in Practice because there is no way to deplete the AIs HP 100%. If anyone can confirm or knows an easy way to perform this leave a comment and I can update.
***Edit Ravenblade stated he was able to do it with a second controller by basically putting the controller on the floor and tapping a button to have the second player keep attacking.
***Update I just got this on my Boosting account
BWS Boosted, basically when the enemy gets down to about one tick (the last line on the health bar) I basically just spammed the ability. In turn when they went to attack I countered/parried and dropped a small bomb. Hope that helps everyone.