Infinite Rez
Someone who goes by the moniker woofmute
figured out how to add custom music to Rez.
The track they used is squarely in #IFYKYK territory.
Here’s another video of woofmute
tinkering with the final release of Rez for the Sega Dreamcast in debug mode:
And here’s a series of bonus videos from the early development stages when it was known as K-Project:
Seeing the process of how a masterpiece comes into existence is just sheer joy.