Knuckle-Dragger Platinum | Prototype
This one requires a lot of luck. At the start, try to hit several of the soldiers in the street below with Hammerfist Elbow Slam. Then, look for a tank, which is denoted by a red skull icon on the mini-map. When a tank appears, Sprint, Jump, and Airdash toward it and perform a string of basic attacks to bust the tank. Succeeding here really involves luck, since tanks seem to spawn randomly.
The easy way to achieve a Platinum score requires a bit of preparation and is somewhat exploitive. First, hijack five or six tanks and park them along one side of the building that the event marker is on. Bust the tanks up a bit, take note of which side of the building they are parked, and then start the event. At the start of the event, drop down the side of the building where the tanks are parked and hit them with Hammerfist Smackdown and basic attacks. Once all of the prepared tanks have been destroyed, target the soldiers and marked tanks and kill them in an attempt to reach the target score.
This video is from our unofficial game guide. You can view the full guide here