Almost every instrumental song variation in Tsukutte Utau: Saru Band (つくってうたう さるバンド) (~6 hours long)
Please read:
Yes, I actually did it all the way through unaware it'd take this long. Now almost all the day is gone thanks to these stupid monkeys :[ . Well I praise the developers of this game muu muu and Nintendo, it must have taken them ages to actually compose all those variations, even if they used bots. ^-^ There are 403 songs in the ROM.
This is labelled almost just because half way through I lost my attention span, so around 1-5 or more songs I accidentally skipped. Next time I should just use a joining script, so stay tuned.
For your convenience, I listened to the base songs first (a fraction of the total length), as most people wouldn't want to listen to all the song variations right. The song variations are an alteration of the base song, with a different pitch or spin on it, etc.
As for the vocal songs there are far too many, as you can give the monkeys words to sing yourself (like the Tomodachi Collection/Life series).