Ok this is a glitch I recently discovered. If this has been found before then disregard but it is kinda cool to do one time. (I did it three times to test it and it worked every time)

Start the last level where you finally kill Mei-oh. Input the debug code and activate "The World" (Teleport). Now go through the entire level as you normally would, until you get to the last room before Mei-oh where the concrete block slides back to reveal the opening for the final battle. what you want to do is teleport behind or on one of the sides of that concrete block. If you do this correctly you will skip the cutscene of the rock sliding back and you won't hear the princess. The rock is hollow though and you can go in the hole. Now you find yourself in Mei-oh's dungeon with music and all but no Mei-oh. Unfortunately there is no way out of here so you'll have to restart but at least you can explore it a little since you are usually too busy fighting for your life. I thought this was pretty cool and hopefully you'll enjoy it.

That's not a glitch since you are uising codes such as the debug code.Maybe the game data cannot be readed correctly when doing that.

It's a glitch because the stone block is hollow.