Ben 10 Galactic Racing

Pick single race then "Primus Dominus" circuit then "Havoc Highway".
This achievement picture is incorrect it is for a 3X stunt combo.

At the first jump right after you start use your right joystick and press up for front flip down for back flip right to roll right left to role left in any order but you cant use the same stunt twice or it won't count for your combo. If you don't have it I recommend doing the 4X combo on this jump (Omni-Trickster achievement)

The combos do not stack if you get the 4X combo achievement you will not unlock your 3X or 2X combos but you will come to another jump later (the last jump before the end of the lap you will jump through a circular rock and there are 4 spinning circular light platforms below) this jump is only big enough to do a 3X combo. This is also a good level to get the 2X combo as well because almost every jump in the level is big enough to do 2 stunts.