EnemySpawner.cs

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

public class EnemySpawner : MonoBehaviour
{
    BasicEnemyMovement basicEnemyMovementScript;

    [SerializeField]
    private List<GameObject> EnemyList = new List<GameObject>();
    [SerializeField]
    private GameObject Enemy1;
    [SerializeField]
    private GameObject Enemy2;
    [SerializeField]
    private GameObject Enemy3;

    public int EnemyIndex = 0;

    public float timer = 2;

    void Start()
    {
        EnemyList.Add(Instantiate(Enemy1));
        EnemyList.Add(Instantiate(Enemy2));
        EnemyList.Add(Instantiate(Enemy3));

        print(String.Format("There are {} enemies", EnemyList.Count));
    }

    void Update()
    {
        timer -= Time.deltaTime;
        if (timer < 0)
        {
            Debug.Log("Enemy timer");
            ChooseNextEnemy();
            timer = 2;
        }

    }

    void ChooseNextEnemy()
    {
        if (EnemyIndex >= EnemyList.Count)
        {
            EnemyIndex = 0;
        }

        basicEnemyMovementScript = EnemyList[EnemyIndex++].GetComponent<BasicEnemyMovement>();

        basicEnemyMovementScript.StartEnemyMovement();
    }
}