When in doubt, add another car.
The best way to make a video of an awesome car even better is to add another car of roughly equal awesomeness. This was the recipe for the video you're about to see. Take one Mercedes-Benz CLK63 AMG Black Series, add a C63 AMG Black Series and a dash of Green Hell. There you have it. The cars were reportedly doing some testing for Mercedes, although we don't actually know what specifically about them was being tested.
What we do know is that the pair sounds great, and the exact reasoning behind the testing isn't all that important when it looks and sounds this cool.