Okay you need to start qualifying these threads a bit more because there are tonnes of utterly broken things like Silver Surfer or one of the Terminator games and such.
But for a game thats actually possible? A game that is fully functioning and worth playing?
Ghouls N Ghosts bar none. THE hardest game on the NES that isn't totally broken. Ninja Gaiden? No, you get a life bar there.
Edit: Was tempted to say the real Super Mario Bros 2 but thats kinda... idk.. when I play it feels more like it's just not really that well designed, lots of beginners traps and placements of enemies just over blind jumps and such.
But for a game thats actually possible? A game that is fully functioning and worth playing?
Ghouls N Ghosts bar none. THE hardest game on the NES that isn't totally broken. Ninja Gaiden? No, you get a life bar there.
Edit: Was tempted to say the real Super Mario Bros 2 but thats kinda... idk.. when I play it feels more like it's just not really that well designed, lots of beginners traps and placements of enemies just over blind jumps and such.