Global Godot Singleton - Without Auto Loading

singleton.gd

extends Node2D
class_name MySingleton

var hello_world: String = "Hello World!";

static var _instance: MySingleton;

static func instance() -> MySingleton:
  if (!_instance):
    _instance = MySingleton.new();

  return _instance;
  
func print_hello():
  print(hello_world);

usage.gd

func _ready():
  MySingleton.instance().print_hello();