Class WaveInstantiate {
    private EnemyMovement enemymovement;

    public void MakeEnemy(Vector3 pos, Quaternion rot, Enemy.EnemyMove behaviour) {
        GameObject enemy = Instantiate (ship, pos, rot) as GameObject;
        enemy.GetComponent<Enemy> ().moveEnemy = behaviour;
    }

    public IEnumerator Wave1() {
        // Set spawn spots and no. of enemies
        // Make the calls to: MakeEnemy(pos, rot, enemymovement.SomeFunctionToMoveEnemy)
    }

    public IEnumerator Wave2() // etc
}

Class Enemy {
    public delegate IEnumerator EnemyMove(Enemy enemy);
    public EnemyMove moveEnemy;

    void Start() {
        // Do some setup

        StartCoroutine(moveEnemy (this));
    }
}

Class EnemyMovement {
    private BulletPatterns bulletpatterns;

    public IEnumerator ForwardThenBack(Enemy enemy) {
        // Move object forward
        yield return StartCoroutine(bulletpatterns.BulletsAtPlayer (enemy.rigidbody.position));
        // Move object back
    }

    // Define some other movements here also
}

Class BulletPatterns {
    private GameObject playerShip;

    public IEnumerator BulletsAtPlayer(Vector3 spawnPos) {
        // Create some bullets that are being aimed at the player
    }
}