I got this after you do the cloud city level after the Queen gives you the lightning staff thing and are back at the academy. While Mags is inspecting your vehicle she tells you to speak to Buzz.
He will tell you to kill 50 greebles by only using Spitfires fire tornado attack. You may have to be supercharged if i remember so make sure you put his car on if you need to.
So turn the handle 3x to drop 3 enemies down then just press Y (assuming you have purchased the upgrade!!!) a few times to eliminate them after a little while. Keep going till you kill 50 then this achievement should pop