По Людски через делегата.... ))

/////////////
// По Людски через делегата....
/////

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

public class GameController : MonoBehaviour
{
    delegate void DoWork();
    DoWork doMyWork;

    public GameObject hazard;
    public Vector3 spawnValues = new Vector3(6, 0, 16);
    public float spawnWait = .5f;
    public float wait = 1;
    public int hazardCount = 10;

    float nextTime;

    // Use this for initialization
    void Start ()
    {
        nextTime = Time.time + wait;
        doMyWork = SpawnWaves;
    }

    void SpawnWaves()
    {
        if (hazardCount > 0 && Time.time > nextTime)
        {
            hazardCount--;
            nextTime = Time.time + spawnWait;

            Vector3 spawnPosition = new Vector3(
                Random.Range(-spawnValues.x, spawnValues.x),
                spawnValues.y, spawnValues.z);

            Quaternion spawnRotation = Quaternion.identity;
            Instantiate(hazard, spawnPosition, spawnRotation);
        }
        else if (hazardCount < 1)
        {
            doMyWork = EmptyDo;
        }
    }

    void EmptyDo()
    {

    }

    // Update is called once per frame
    void Update()
    {
        // делегат
        doMyWork();
    }
}


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/////////
// место вот этого что предлагают в уроке - через Абстрактное АПИ
// и хитрые конструкции....
///

void Start ()
{
    StartCoroutine (SpawnWaves ());
}

IEnumerator SpawnWaves ()
{
    yield return new WaitForSeconds (startWait);
    while (true)
    {
        for (int i = 0; i < hazardCount; i++)
        {
            Vector3 spawnPosition = new Vector3 (Random.Range (-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
            Quaternion spawnRotation = Quaternion.identity;
            Instantiate (hazard, spawnPosition, spawnRotation);
            yield return new WaitForSeconds (spawnWait);
        }
        yield return new WaitForSeconds (waveWait);
    }
}