You can get a two-in-one achievement here easily(if you haven't done the other one already.) Go on to Phu Temples Freestyle either stage 9 or 10, then from the off hold the multiplier from the first ramp to the first ramp going into the rock crevices bit...seems hard but it really isn't, just keep hitting boost and obviously using fresh tricks, by the time you get there with that multiplier, should be about a x9 with a special trick probably, there are some huge jumps, then you will also unlock "Killer combo" too, this was the best method for me anyway.