Thought I encountered an error until I realized the spawning scene needed to be autoloaded. You should look into using an EditorPlugin script to automatically load it with the add_autoload_singleton() method. Then anywhere it needs to be used do get_tree().root.get_node_or_null("AutoloadName") to check if it exists. You can also load custom nodes with add_custom_type() to make stuff appear in the node menu without using class_name. Sorry if you already know this and this is redundant info, just trying to help. Anyway... Other than that cool project! 😁