This is obtained on the first mission of the game. It's the battle after you talk to Kat for the first time. You will see a large gyrating environmental hazard above you. Walk up close to it and let enemies come up to you. Press
to launch them into the air into the Hurricane ride. Be careful not to hold
, as it will launch you into the air and possibly damage you as well. You'll know it killed one of them when you see "Environmental Kill" on the right side of the screen. On human, demon hunter, or nephilim difficulty there are exactly 10 enemies in the area, so if you accidentally kill one of them not using the ride you can restart from checkpoint, although this will count as a "Death" against your mission ranking at the end.