Exit the game and access our example code's Assets folder; move the enemy.png file into our Sprites folder.

Following that, drag-and-drop it into your scene from the Scene tab to place it in the level.

Right-click on the Scripts folder you created earlier, click on Create, and select the C# Script label. Call this new script MoveTowardsPlayer. Go to MonoDevelop and use the following code:

using UnityEngine;
using System.Collections;

public class MoveTowardsPlayer : MonoBehaviour 
{
  private Transform player;
  public float speed = 2.0f;

  // Use this for initialization
  void Start () 
  {
    player = GameObject.Find("playerShip").transform;
  }
  
  // Update is called once per frame
  void Update () 
  {
    Vector3 delta = player.position - transform.position;
    delta.Normalize();
    float moveSpeed = speed * Time.deltaTime;
    transform.position = transform.position + (delta * moveSpeed);
  }
}

In the beginning of the game, I find the player ship and get his transform component. Then, in every frame of the project, we move the enemy from where it currently is to the direction where the player is at.

Drag-and-drop this newly added behavior onto our enemy object.

Next, add a circle collider to our enemy by going to Component | Physics 2D | Circle Collider 2D. Change the Radius property to .455, and run the game. Have a look at the following screenshot:

Right-click on the Scripts folder you created earlier, click on Create, and select the C# Script label. Call this new script EnemyBehaviour. Go to MonoDevelop, and use the following code:

using UnityEngine; // MonoBehaviour

public class EnemyBehaviour : MonoBehaviour 
{

  // How many times should I be hit before I die
  public int health = 2;

  void OnCollisionEnter2D(Collision2D theCollision)
  {
    // Uncomment this line to check for collision
    //Debug.Log("Hit"+ theCollision.gameObject.name);

    // this line looks for "laser" in the names of 
    // anything collided.
    if(theCollision.gameObject.name.Contains("laser"))
    {
      LaserBehaviour laser = theCollision.gameObject.GetComponent("LaserBehaviour") as LaserBehaviour;
      health -= laser.damage;
      Destroy (theCollision.gameObject);
    }
    
    if (health <= 0) 
    {
      Destroy (this.gameObject);
    }
  }
}

Now, you will notice that we have commented a line of code calling the function Debug.Log. This function will print something onto your console, which may help you when debugging your own code in the future.

Save the file, and then go back into Unity. Attach the EnemyBehaviour behavior to your enemy object. For collision events to register we need to add a Rigidbody 2D component to our enemy by going to Component | Physics 2D | Rigidbody 2D. Change the Gravity Scale to 0 so it will not fall. Have a look at the following screenshot: