Holy necrothread, Batman!
Among the hardest games I’ve beaten (legit, on original hardware, with no codes or cheat devices)
Ninja Gaiden 1-3 - I could blow through NG2 easy. I beat the other 2 but I found them much harder.
The Adventures Of Bayou Billy - an exercise in patience and perseverance.
Blaster Master
Batman (NES)
Fester’s Quest - again, took a LOT of patience.
Mega Man 1-9 - First one is still the hardest.
Castlevania 1 & 3 - first one is hard as balls. I could beat CV3 regularly, though. Didn’t include Simon’s Quest because I only beat it on an emulator.
TMNT (NES) - beat it once using the “collect a shitload of scrolls” trick.
The Revenge Of Shinobi - beat it on original hardware with the good ending. Not easy.
Shadow Dancer & Shinobi 3
Contra, Super C, Operation C, Contra 3, Contra Shattered Soldier
Mega Man X 1-3