Master JugglerG 10

I found a really easy way to get this achievement in the Warren dungeon which you have to go in on the way to E Tower in the main story. You will be collecting 4 parts to build a flyer bot ,after gaining the second part from a chest it will show a door being opened to your right. When you go through this door you will see a bunch of small flying red enemies making a barrier so you can't go through to the green objective marker. Basically there are red enemies flying above this so as soon as you shoot a enemy in the barrier with red lasers they will be replaced straight away by one of the enemies flying above the door, so all I did was just keep shooting the bottom right two and they would get replaced with new enemies flying above. Keep shooting until you hit 40x combo. I have just tested and can confirm this works after you have cleared this dungeon in the story!

Check out the video below thanks to Maka!

https://www.youtube.com/watch?v=rQhnX61d1bI