Enemy Boss movement AI

Good day to all, I am trying to get an enemy boss ship to appear on screen and attack my ship and also dodge my attacks sometimes. So far I have gotten him to attack my ship but hes stays on the edge of the screen. Here is my code :

#pragma strict

// here are public variables for the enemy ship that can be accessed in the inspector
var health:int = 2;
var explosion:GameObject;
var expOrb:GameObject;
var enemyBullet:GameObject;
var expDrop:int = 3;
var hitSound:AudioClip;
var fireRate:float = 2.0;

//heres the private variable counter to keep track of time for fire rate.
private var counter:float = 0.0;

function Update () {
//here we make counter count based on time for the fire rate
counter += Time.deltaTime;

//if the ship goes too far left, we destroy it.
if(transform.position.x < -12){

//here we shoot 4 bullets if the counter counts higher than the fire rate.
if(counter > fireRate){
var custom1 = Instantiate(enemyBullet, transform.position - Vector3(0.5,0.1,0), Quaternion.Euler(-90,0,0));
var custom2 = Instantiate(enemyBullet, transform.position - Vector3(0.5,0.1,0), Quaternion.Euler(-90,0,0));
var custom3 = Instantiate(enemyBullet, transform.position- Vector3(0.5,0.1,0), Quaternion.Euler(-90,0,0));
var custom4 = Instantiate(enemyBullet, transform.position- Vector3(0.5,0.1,0), Quaternion.Euler(-90,0,0));
//to make the bullets spread, we add extra z velocity to each one to they all move on their own path.
custom1.rigidbody.velocity.z = 3;
custom2.rigidbody.velocity.z = 1;
custom3.rigidbody.velocity.z = -1;
custom4.rigidbody.velocity.z = -3;
counter = 0.0;

//end of function update

//if a bullet hits the ship, the bullets sends us the hit message to trigger this function to bring down the ships health
function hit () {
health -= 1;
if(health != 0){
if(audio.enabled == true){
if(health <= 0){

//if health is 0, then this function is triggered to spawn some orbs, spawn the explosion animation object, and destroy itself
function onDeath () {
expDrop -= 1;
if(expDrop <= 0){
if(expDrop > 0){

How do i add the movement aspect to it?

The AI needs to cover out these basic steps

  1. Detect the bullet
  2. Calculate where the bullet is going to be in time
  3. Move away from the bullets location

If there is more then one bullet on the screen then you can run through the steps multiple times and work out a safe location to move too.