You will get this at the end of the third level. During the level you will have to avoid some cameras and guards. All very easy. Remember to collect all the item boxes. They are very hard to miss though.
At the end there is another fight with your dragon. First against Shadow, then some mechas will appear.
Just make combos with X and Y. For example XXXX, XXYY, YYXX or YYYY. And use the other buttons to move around.
The achievement will unlock, once you are back in your headquarter room.