The first level can be used to complete this twice. The first part of the level when you are going down a rail (Standing and Sliding). As there is slow motion and such hit the signs and barrels as this will net you around 4-5 stars per kill. When you get to the bottom of the rail then use the cart (this will help for cart achievement) shooting who ever you can then before the counter stops go onto the next rail going upwards while shooting more of the environment to kill the enemies by the time your up should have around 50-60 star.
The second part would be at the end when the guys first come out in the bar kill all of them get to the top and keep jumping and such so the slow motion comes as you always get more points for the slow motion the guys will come out 8-9 at a time 2-3 times before the final boss for this level.
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