Simian Shootout is the first stage of the Monkeying Around series in the Challenges for TimeSplitters 2.
World Record Strategy
Start and head straight into the building and to the stairs in the back. You want to get up on the balcony by the bell as fast as possible. As you pass under the bell, a monkey should fly by so shoot it. From there either stand to the left of the right of the bell. Up until about 22 seconds left, the monkeys will randomly appear two at a time from one of three locations: From the right, from the bell, and from the left. Do your best getting combos during this time. One technique is to wait as long as possible to shoot the second monkey in a set so that you can hopefull continue the combo when the next set appears.
After 22 seconds, the order the monkeys appear in is always the same, and you can get a very large combo going. Stand to the right of the bell. A monkey will come from the right, and another from the left. Another will come from the right again, and then another from the left. Next, one will come from the bell tower, followed by one from the left. Right after you shoot that one, a monkey from the right will appear in your lower view. Shoot it while still facing to the left. Another monkey will come out of the bell tower, and then another from the left. After that another monkey from the right will again appear in the lower part of the screen. Shoot it while still facing left. After that, three straight monkeys will appear from the bell tower. Shoot the first two quickly, then immediately move to the center of the bell tower and look out and aim out over the courtyard. The third monkey will shoot out. Wait a bit until it starts on it's downward arc and shoot it. Using the aim function helps. You absolutely need to delay a bit on shooting this last one.
After shooting the third bell monkey, dash over to the very left side of the balcony and aim at where the monkeys appear from that side. Two monkeys will appear. Shoot them. If you delayed you shot correctly on the third bell monkey, you will just barely be able to continue you huge combo. After shooting these two monkeys, immediately do a 180 and make an almost blind two shots at the monkeys that are coming from the right. Pray auto aim is on your side and you'll get them. Now you're done. Wasn't that easy?
Watching a video helps for this stage as the whole large combo happens fast and you must be smooth to pull it off correctly. Practice...