HUD.cs

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

public class HUD : MonoBehaviour
{
    private void OnGUI()
    {
        GUI.Box(new Rect(10, 10, 100, 90),
            $"HP: {GameSystem.HP}\n " +
            $"Money: {GameSystem.Money}\n " +
            $"Monsters: {GameSystem.MonsterCount}");
    }
}