I need to make a burnout or skid mark type of effects. I have an object that starts in one direction and then quickly jets the other way.
Over your plain layer, create a layer with the full-length skid marks (which could be the original background retouched in Photoshop or a pair of masked solids with feathered edges in Multiply mode, or however). Set its alpha matte to another solid, which has a moving Bezier mask to gradually reveal the skidmark layer (at the last position, draw the curve, set a keyframe; go to first frame where it occurs, and adjust the mask so only the first bit is showing.). You may have to do some tweening to sync the speed of the object, and/or adjustment of the area where it meets the wheels/etc.
