The best way to get the achievement is in mission 2 on Legendary Dark Knight mode with Trish/Lady. You need a ready Devil Trigger before you get in the warehouse from the bridge control. If you are in the warehaouse from the bridge control pull all enemys toghter and use the Devil Trigger.
Her is a Video to see it works:
Sorry, this Game Clip has been removed
i hope the guide help a lot.