Space Shooter Enemy AI Maneuver Script

Hello and thank you in advance for any help or advice you can share with me.

I am a newbie, but I am going well so far. After the space shooter tutorial I've decided to build one of my own that would combine 3D objects in a 2D atmosphere. And fairly I have succeded. The problem is that I stuck with enemy maneuvering script. Unity tutorial had files regarding simple enemy maneuvering (Done_EvasiveManeuver.cs), but Unity's game has been built in 3D with Z-axis as a main axis. I have translated C# into Java and I am looking at this script and I do not see neither undestand what could be changed to achieve proper maneuvering on X and Y axes. I am suspecting that it might not be entirely because of the axes. Or maybe yes - Unity yells at me that he is "MissingFieldException: UnityEngine.Vector2.z"

What I am trying to achieve is an object coming from the right side of the screen and just change it trajectory.

Coud you at least point me in the right direction. I am trying to tackle this for a week or so, reading related materials and forums, but I may have missed something.

 //fire control
 var shot : GameObject;
 var shotSpawnPoint : Transform;
 var fireRate : float;
 var delay : float;
 var soundRandomizer: AudioClip[];
 
 //Maneuvering
 var boundary : Boundary;
 var dodge : float;
 var smoothing : float;
 var startWait : Vector2;
 var maneuverTime : Vector2;
 var maneuverWait : Vector2;
 var currentSpeed : float;
 var targetManeuver : float;
 
 
 function Start () {
 
     InvokeRepeating ("Fire", delay, fireRate);
     
     currentSpeed = rigidbody2D.velocity.x;
     StartCoroutine(Evade());
 
 }
     
 function FixedUpdate (){
         var newManeuver = Mathf.MoveTowards (rigidbody2D.velocity.x, targetManeuver, smoothing * Time.deltaTime);
         rigidbody2D.velocity = new Vector2 (currentSpeed, newManeuver);
         rigidbody2D.position = new Vector2
         (
             Mathf.Clamp(rigidbody2D.position.x, boundary.xMin, boundary.xMax), 
             Mathf.Clamp(rigidbody2D.position.y, boundary.yMin, boundary.yMax)
         );
 }
 
 function Evade (){
         yield WaitForSeconds (Random.Range (startWait.x, startWait.y));
         while (true)
         {
             targetManeuver = Random.Range (1, dodge) * -Mathf.Sign (transform.position.x);
             yield WaitForSeconds (Random.Range (maneuverTime.x, maneuverTime.y));
             targetManeuver = 0;
             yield WaitForSeconds (Random.Range (maneuverWait.x, maneuverWait.y));
         }
 }
 
 function Fire () {
 
         Instantiate(shot, shotSpawnPoint.position, shotSpawnPoint.rotation);
         audio.clip = soundRandomizer[Random.Range(0,soundRandomizer.length)];
         audio.Play();
 }