If you found this game via browsing itch.io, here is a quick rundown on why every comment here is about Shaggy x Matt: If you beat FNF Shaggy X Matt, You get a letter in Freeplay. This prompts you to install homebrew on the Freeplay menu. If you accept, you can launch the homebrew channel. Once you do, you will be thrown into a harder version of the final song with death notes (from Vs Tricky) and Danger notes (from FNF HD). If you (somehow) beat that, you get sent here.
TL;DR: You get sent here if you beat the extra challenge in Friday Night Funkin Shaggy X Matt