Bonus Round is based around the classic Street Fighter II stage where you beat the ever-loving s#^t out of inanimate objects (like a car!). Just going absolutely sicko mode on that bad boy. Goonhammer has a deep commitment to accuracy in reporting. In theory, you could play this with any other type of roughly car-shaped model, I guess, but you really should use the official model.
Chapter Approved 2019 released rules for Linked Games, which you can read about in the Goonhammer preview here. This mission is designed to be the perfect interlude, played between the first and second turns during the game’s third battle round, i.e. halfway through the game. Pause the game and play a game of Kill Team using the Bonus Round, Goonhammer approved, mission. When you return to the game of 40k, the winner of the Bonus Round scores D3 victory points in that game, and immediately gains D3 CP.
Read more about this mission here!