Congratulations! You've essentially beaten MKF! World 0 (the final world that requires the 9 World Keys to enter) is still in the works.
Be sure to go back to the 9 Worlds and see if you've completed all the available levels. The Black Switch Palace unlocks at least 1 level per World. They're usually some of the most challenging in the game.
There are several Sonic Skins you can download here: https://drive.google.com/drive/folders/1DdPxbCkdaK2pPv-GA9YRKXQRk_Lv_gky
I strongly recommend the Legacy_Sonic3_Reskin.zip that "the_swordsman_ps4" (on Discord) and I made together. It's basically a Sonic 3 inspired set of sprites for Sonic. They were used in previous versions in the game, but a few months ago were updated to the most current version. (Actually, I still need to fix his Controls Sheet... I need to get back to that).
Lab of the fusionist and the bug is more than just the music not working.
Sounds to me like you have may have not downloaded all the latest Music files. When music files are missing, it can affect more than just music not playing. Download the latest MKF V0.91 - MUSIC ONLY file and unzip it into your game directory.
The letters for the puzzle of one of the jigsaws does not appear. I cant pass the stage.
Known bug that will be fixed in the next update.
