Debug Mode is a game mode accessible via running the game in RPG Maker, that allows you to take advantage of certain in-game exploits designed to aid authors in testing their worlds.
It can be accessed via Noclip Mode, a nickname for running the game in RPG Maker, that allows you to walk through solid, unwalkable tiles by holding down the Ctrl key (Or ⌘ on a Mac (needs confirmation)), and from there by stepping on a special tile somewhere outside the walls of Urotsuki's Room in the real world, that may change based on the version. You will hear a short jingle when you step on the right tile.