I guess one way to do it would be to make two variables
MouseYdeviation
MouseXdeviation
Every tick set mouseYdeviation : MouseYdeviation+choose(-3,-2,-1,1,2,3)
Every tick set mouseXdeviation : MouseXdeviation+choose(-3,-2,-1,1,2,3)
And set the crosshair to mouse.x+MouseXdeviation , mouse.y+MouseYdeviation
Maybe using clamp to prevent it from deviating too much..