GameFAQs users have Castlevania rated as a 4.09/5 on the difficulty scale, so this would likely be the hardest game I have beaten (in their eyes at least.) However, a game with unlimited continues should not be considered one of the harder games ever made.
For me, beating Pitfall on the Genesis was an accomplishment. I dunno how the f I was able to beat that game. no strategy guide or walkthroughs, Youtube was barely a thing at the time. I feel lucky to have beaten it. I dont remember what difficulty I had it set to but typically I just go with Normal.
Gargoyle's Quest II is another one that again I have no clue how I was able to finish. Some of the boss fights were really tough. I guess the game was fun enough and I liked the setting and the characters enough to persevere.
I would love to hear about your gaming feats. This is youtter moment to brag to the world about your awesomeness