I wanted to try myself at ROM disassembly and recently I've been trying to beat Bird Week, the most hardest official NES/Famicom game created in the lifetime of the console. This resulted in game disassembling with the purpose to find out some bugs/exploits which would help me to complete the game. Seems that there are none that would help the player to ease the game completion, but at lease I've re-created the game's source code 
I've used DISASM6 v1.5 to create the initial source code, with FCEUX code/data log provided to separate code from data.
Link: https://github.com/Mistranger/birdweeksource
To compile the source, you should use ASM6. After successful compilation you should get a ROM file identical to "Bird Week (J) [!].nes"
If you're unfamiliar with Bird Week, I recommend checking out this TOP10 Hardest NES games: https://www.youtube.com/watch?v=l6_vKhrJ_3c (in Russian but English subtitles available)
The people who composed this top spent 3 years compiling it, beating all the games presented there without savestates and cheating.
So, if you want to try out Bird Week, I would wish you only luck and nothing more
I've used DISASM6 v1.5 to create the initial source code, with FCEUX code/data log provided to separate code from data.
Link: https://github.com/Mistranger/birdweeksource
To compile the source, you should use ASM6. After successful compilation you should get a ROM file identical to "Bird Week (J) [!].nes"
If you're unfamiliar with Bird Week, I recommend checking out this TOP10 Hardest NES games: https://www.youtube.com/watch?v=l6_vKhrJ_3c (in Russian but English subtitles available)
The people who composed this top spent 3 years compiling it, beating all the games presented there without savestates and cheating.
So, if you want to try out Bird Week, I would wish you only luck and nothing more