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enemy
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using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Enemy : MonoBehaviour
{
    public float move_speed;
    public Transform enemy;
    public GameObject player;

    void Awake()
    {
        move_speed = (Random.Range(1, 5));
    }

    void Update()
    {
        enemy.position += transform.right * Time.deltaTime * move_speed;
        if (Input.GetMouseButtonDown(0))
        {
            Vector3 MousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            if (MousePos.x < 0.0f)
            {
                Destroy(this.gameObject);
            }
        }

        if (enemy.position.x > -0.35f)
        {
            Destroy(gameObject);
            Destroy(player);
        }
    }
}

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spawn
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using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class EnemyManager : MonoBehaviour
{
    public GameObject enemy_prefab;
    public List<GameObject> enemy;
    public float delayBetweenWaves = 15f;
    public int currentWave = 1;
    public Vector3 spawn_point;
    public Vector3 enemy_look;

    public float cellX = 1f;
    public float cellY = 1f;

    public bool waitForEnemys = true;

    void Start()
    {
        Spawn();
    }

    void Update()
    {
        if (waitForEnemys) return;

        if (enemy.Count == 0)
        {
            currentWave++;
            waitForEnemys = true;
            StartCoroutine(NextWave());
        }
    }


    private void Spawn()
    {
        enemy.Clear();
        int enemyCount = currentWave * 3;
        for (int i = 0; i < enemyCount; i++)
        {
            GameObject z = (GameObject)Instantiate(enemy_prefab,
                                                   GetSpawnPoint(i, enemyCount),
                                                   GetSpawnDirection(i));
            enemy.Add(z);
        }
        waitForEnemys = false;
    }

    private Quaternion GetSpawnDirection(int num)
    {
        return Quaternion.Euler(enemy_look - spawn_point);
    }

    private Vector3 GetSpawnPoint(int num, int max)
    {
        int q1 = (int)Mathf.Sqrt(max);
        float q2 = Mathf.Sqrt(max);
        q1 = (q1 != q2 ? q1 + 1 : q1);

        return (spawn_point +
            new Vector3(cellX * (num % q1),
            0f,
            cellY * (num / q1)));
    }

    IEnumerator NextWave()
    {
        float time = 0;
        do
        {
            time += Time.deltaTime;
            yield return null;
        } while (time < delayBetweenWaves);
        Spawn();
    }

}