Bionic Commando

A required task for completing the campaign, you need to destroy a single biomech to complete the Fair Fight! challenge. These are first encountered after you earn the Death From Above ability and take on the wave of paratroopers that arrives. Once the paratroopers are finished, use the inactive mines to reach a tunnel, and after a brief grunt encounter you'll meet your first pair of biomechs.

If you can get above them, use Death From Above to weaken them before taking them on directly. If you're on the same level as the biomech, use the LB button to dodge around until you get behind them. Use LT to latch on to their backs with your bionic arm (watch for the crosshair to turn red) and tap A twice to perform the zip-kick move on them. Repeat as needed to take them down. Using this method you'll also earn two hand-to-hand biomech kills that will contribute to three required for the following Achievement: