MonsterController.cs

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

public class MonsterController : MonoBehaviour
{
    // Start is called before the first frame update
    public GameObject target;
    private NavMeshAgent bot;
    public int damage = 10;
    public int hp = 100;
    private float name_margin = 1f;
    private Color startColor;
    Renderer render;
    void Start()
    {
        target = GameObject.FindGameObjectWithTag("Base");

        bot = GetComponent<NavMeshAgent>();
        bot.destination = target.transform.position;
        render = gameObject.GetComponent<Renderer>();
        startColor = render.material.color;
    }
    private void Update()
    {
        if(hp <= 0)
        {
            Destroy(gameObject);
        }
    }
    void OnTriggerEnter(Collider col)
    {
        Debug.Log(col.gameObject);

        if(col.gameObject.tag == "Base")
        {
            GameSystem.HP -= damage;
            Destroy(gameObject);
        }
    }

    private void OnGUI()
    {
        Vector3 pos = new Vector3(transform.position.x - name_margin,
            transform.position.y,
            transform.position.z);
        Vector3 crd = Camera.main.WorldToScreenPoint(pos);
        crd.y = Screen.height - crd.y;

        GUIStyle style = new GUIStyle();
        style.fontSize = 12;
        style.normal.textColor = Color.red;
        style.alignment = TextAnchor.MiddleCenter;
        float hpPercent = (float)hp/100 * 100;
        GUI.Label(new Rect(
            crd.x - 50, crd.y, 100, 20),
            $"Monster {hpPercent}%", style);
    }

    public void ReturnColor()
    {
        render.material.color = startColor;
    }
    public void AttackIndicate()
    {

        render.material.color = Color.red;
        Invoke("ReturnColor", 0.5f);

    }
}