the way Rare do things. [...] We sorta wanted to stylize her up a bit and make her more iconic". However, the designers ultimately decided to tone down the styling of the game a bit. The Xbox 360 gave the developers more possibilities to include what they always wanted and allowed them to create the game's co-operative mode, which was one of the first that could be played via Xbox Live. Designing the co-operative mode over Xbox Live was very challenging for the developers. According to Duncan Botwood, who was responsible for most of the multiplayer, "it was quite an effort to put it in, to be honest. You have to cater for a number of eventualities you just don't get normally. We think we pulled it off, and because we pulled it off, other people might feel inspired to put the effort in, and we think that's a good thing". Perfect Dark Zero is also one of the first games that uses Havok's HydraCore physics engine, which was specifically designed for multi-core video game systems like the Xbox 360. The game's renderer engine employs more advanced graphic technologies than was possible in the previous console generation, including parallax mapping, ambient occlusion, subsurface scattering, and high dynamic range. The soundtrack of the game was primarily composed by David Clynick, who worked with Grant Kirkhope on the original Nintendo 64 game's score. New York-based group MorissonPoe contributed two songs to the score—the opening theme song "Glitter Girl (Evil Side)" and the closing credits theme "Pearl Necklace"—while DJs Kepi and Kat composed the game's nightclub theme. The cover mode was designed to enhance the stealth aspect of the game and the third-person perspective was needed to allow players to see the character they were playing. The idea of bringing the game into a total third-person perspective was rejected as the shooting "works better" in first-person view, explained Tilston. Developers decided not to include a jumping function since they felt it goes against the nature of the genre. Botwood pointed out that it can "look damn stupid when you see other players doing it". For this reason, the team implemented moves such as climbing obstacles or, more specifically, the combat roll, which makes players harder to hit since it breaks the game's auto-aim lock. The transition between first and third-person view with some moves took a lot of work so that they did