During the Creepy Crypt Stage, it is possible to enter through the "Exit" gate near the end of the underground crypt portion of the level, even with the purple fence meant to stop you from doing so until you acquire the Tome. Getting up next to the purple fence still allows you to get the input prompt to exit the crypt.

If you reenter the crypt to try to get the tome, you are unable to get back into the crypt as the purple fence blocks your path, and it is possible to get stuck permanently between the fence and some of the blocks on the edge of the platform, forcing you to go back to the main menu/ camp manually without completing the stage.

I am unsure if exiting the crypt without getting the tome makes it so you can't properly complete the level, as I got stuck before I could test that out, and I don't have the time to recreate the glitch.