public Transform Target;
    public Vector3 MoveDirection;
    public AnimationCurve CurveAnim;
    float curveTime;
    void Start () {
        MoveDirection = Target.position - transform.position;
        MoveDirection = MoveDirection.normalized;
        CurveAnim = new AnimationCurve
            (new Keyframe(0, -1), new Keyframe(1, 1), new Keyframe(2, -1));
        CurveAnim.preWrapMode = WrapMode.Loop;
        CurveAnim.postWrapMode = WrapMode.Loop;
    }
    void Update () {
        transform.Translate(MoveDirection * Time.deltaTime);
        curveTime += Time.deltaTime;
        transform.position = new Vector3(transform.position.x, CurveAnim.Evaluate(curveTime), 0);
    }