I get a real kick out of tracing music back to its roots, and with the Lemon Demon FNF mod the musical lineage is actually pretty clear. The songs that show up in that mod are originally by Neil Cicierega under his music project 'Lemon Demon' — yes, the same creative force behind tracks like 'The Ultimate Showdown of Ultimate Destiny' and 'Brodyquest'. His quirky, melodically sharp style is what makes those tracks such a natural fit for a rhythm game vibe.
The mod itself is a fan-made creation built on top of 'Friday Night Funkin''. A handful of community modders usually handle charting the notes, making sprites, coding the engine tweaks, and sometimes remixing the original Lemon Demon tracks to better fit gameplay. Credits for each specific mod release tend to list who did what — the original compositions remain Neil's, but the FNF versions often have new arrangements or edits to match the rhythm mechanics. Personally, I love how the mod community pays homage to musicians like Neil by bringing those songs into a playful, competitive context — it feels like a big group jam session that just happened to find a new stage. Makes me want to queue up the soundtrack and play one more run.