Trajectory aim, how do i do it?

I don't know if this is exactly what you're looking for, but you can use the LineRenderer component to add a ray from the object to the target. Add a LineRenderer (menu Component/Miscellaneous/Line Renderer) to your object and modify the script like below:

private var lineRenderer : LineRenderer;

function Start() { lineRenderer = GetComponent(LineRenderer); lineRenderer.SetColors(Color.red, Color.red); lineRenderer.SetWidth(0.1,0.1); lineRenderer.SetVertexCount(2); }

// speed is the rate at which the object will rotate var speed = 4.0;

function Update () {

 // Generate a plane that intersects the transform's position with an upwards normal.
 var playerPlane = new Plane(Vector3.up, transform.position);
 // Generate a ray from the cursor position
 var ray = Camera.main.ScreenPointToRay (Input.mousePosition);
 // Determine the point where the cursor ray intersects the plane.
 // This will be the point that the object must look towards to be looking at the mouse.
 // Raycasting to a Plane object only gives us a distance, so we'll have to take the distance,
 //   then find the point along that ray that meets that distance.  This will be the point
 //   to look at.
 var hitdist = 0.0;
 // If the ray is parallel to the plane, Raycast will return false.
 if (playerPlane.Raycast(ray, hitdist)) {
     // Get the point along the ray that hits the calculated distance.
     var targetPoint = ray.GetPoint(hitdist);
     // Determine the target rotation.  This is the rotation if the transform looks at the target point.
     var targetRotation = Quaternion.LookRotation(targetPoint - transform.position);
     // Smoothly rotate towards the target point.
     transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
 } else {
     targetPoint = transform.position;
 }
 lineRenderer.SetPosition(0, transform.position);
 lineRenderer.SetPosition(1, targetPoint);

} EDITED: You can stop the ray at walls or other obstacles simply by doing a Linecast from transform.position to targetPoint, and replacing the later with the hit point (if any):

...
        transform.rotation = Quaternion.Slerp(transform.rotation, targetRotation, speed * Time.deltaTime);
        // shorten the ray if it's hitting some obstacle:
        var hit: RaycastHit;
        if (Physics.Linecast(transform.position, targetPoint, hit)){
            targetPoint = hit.point;
        }
    } else {
        targetPoint = transform.position;
    }
    lineRenderer.SetPosition(0, transform.position);
    lineRenderer.SetPosition(1, targetPoint);
}