I have downloaded the game directly from itch.io, and the secret mode and the intro should be working properly.
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My video message, here's what I say when showing the video:
https://drive.google.com/file/d/1psedvBvieP_pEbX4yUwB9uxrqQ1wizfd/vie
I just realized I forgot to include some important details in the instructions sorry XD. Basically, I forgot to mention that you need to enter the special mode, specifically in level 2-1. You have to go to the pit with both the first and second players: the first player must have 6 lives, and the second one must have 9. After that, it should unlock. As for the intro issue, I think the problem is with the name file. I'll try to fix it tomorrow.