You may have heard about the glitch regarding the Manual in Wily Beast and Weakest Creature from the touhou wiki. It mentions there that if you open the Manual 15 or more times, and then you go and select a difficulty and after that return to the difficulty screen, you will be met with a garbled up text. If you select that text and proceed to start the game, you will be playing the Extra stage on Hard difficulty, except there are no enemies and nothing else happens.
I’ve tested this myself and I would like to add few more things which are currently not mentioned there. Upon selecting the garbled text, it will turn into “Lunatic Mode”, although neither the stage location or the difficulty shown in the upper corner are related to Lunatic. When you launch this bugged stage at first you are capable of shooting and bombing, but as soon as you kill an invisible enemy you will stop being able to do anything else than fly around. You will even lose the ability to focus.
Another thing to notice is that once the Manual glitch is active, even if you didn’t trigger the garbled up text yet and you try to go back to the main menu, the Manual option would be selected instead of Game Start.
If you do the Manual glitch and choose Extra Start instead of Game Start, when you go back to the difficulty screen before choosing a character, the difficulty will be gone, showing nothing on the screen. However if you proceed to play it, it will just be a regular Extra stage.
Speaking of difficulties that vanish, if you play the bugged Extra on Hard difficulty and try to go back to the select difficulty screen, it would be empty.