Respawner.cs

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

public class Respawner : MonoBehaviour
{
    public float repeat_time;
    public float curr_time;
    public GameObject monster;

    void Start()
    {
        curr_time = repeat_time;
    }

    void Update()
    {
        if (GameSystem.MonsterCount <= 0)
            return;
        curr_time -= Time.deltaTime;
        if(curr_time <= 0)
        {
            curr_time = repeat_time;
            Instantiate(monster, transform.position, Quaternion.identity);
            GameSystem.MonsterCount--;
        }
    }
}