QWOP, by a wide margin. Reasoning: It's free, go try it.

There is one game, one level, that was so hard to beat that I just gave up and walked away, never to return. The stampede on Lion King from the SNES.

A lot of games from that era were epically hard; few games had a difficulty setting, a lot of tie-ins meant games looked and played polished but no effort was given to make a solid game, computing power meant there was usually only one way to complete a mission or level. However this was a game made for kids and that fucking game, that fucking level was simply bullshit.

There are so many kinds of difficulty that this is hard to answer.

There's fake difficulty, where the game is just being cheap. Some games are hard because their mechanics or controls are just janky.

Some games are easy to lock yourself out of the ending and not know it. Try the game from the start again!

There's genuinely difficult games, but any time a game is difficult in a "fair" sense, there are people on the internet who'll beat it with a guitar controller, or blindfolded, or without any power ups.

If you want a game that not many people could beat...I don't think many people could beat Bokosuka Wars today...

Just try to play Dwarf Fortress, and you'll drop any other opinion on this subject. Especially the ASCII version of the game, not the fancy graphical one.

The original Prince of Persia

Mushihimesama Futari was the hardest game I've ever played, and this is coming from someone who enjoys playing Touhou on Lunatic Mode. My god, the bullets, the sheer amount of bullets! I felt so proud of myself when I finally beat this boss.

Fear and Hunger is a contender. If you aren't aware, imagine a JRPG where you kill god at the end, but you don't ever level up. Also the first enemy you fight is very likely to kill you, and has just as much of a chance of doing so on your 100th playthrough. Oh, and you start from the beginning every time you die.

Probably some of the old Nintendo games. Silver surfer is an extremely difficult bullet hell. Battletoads required insane memorization and timing, pretty sure you had to act before the game even told you in some places.

Shattered Pixel Dungeon with all 9 challenges active. I know there are a few people who have won the game with all 9, but my god is it hard.

Toss up between RC Pro-Am and Ninja Gaiden on the NES. I beat them both and they were both a real bitch. So, so many times I got to the final race or stage and couldn't do it... so you start all over from the beginning.

Games like that don't exist anymore.

I always put the original Blaster Master on the NES up there.

It had no save capability at all, nor any codes to stop & restart later. When you sit down, you better be ready to do the whole 4+ hours in one playthrough (or just leave the NES on & walk away).

But the kicker was that once you got hit just a few times, you might as well restart. The gun (in person mode) would power down with each hit, and after a few hits, well, you just didn't have enough 'oomph' to kill the bosses. But the power-ups to get the gun were fairly sparse in the first place, so once you got hit, it wasn't like you could just retrace your steps & power up again.

Mildly interesting, at least to me, I understand it's been remastered for the Switch. It now has save points AND being hit doesn't reduce your gun's power. That would make it a completely different game. I'm be curious to check it out someday. If nothing else, I'm curious to see how much of it I remember. I suspect I can autopilot the first 2 hours, despite it being 40(?) years later.

Battletoads

don’t starve adventure mode

this cute little game took me years to beat. souls games don’t even come close to it (and I love them very much)

it will throw a wrench into your plans at every step. the designers seem to have worked closely with psychiatrists to make you think you have figured it out only to destroy again and again and again

SLASH'EM

This is a roguelike for people who find Nethack too easy. Then you have the option of layering in challenges like blind, pacifist, and vegan. Go ahead, try playing through as a blind, vegan, pacifist Tourist. I dare ya.

Faster Than Light.

Seriously you could play ten games a day for a year and not even come close to winning, even if you're quite good at it.

Celeste is a truly difficult 2D platformer. VVVVVV follows behind. Metroid Dread is a cruel one.

F-ZERO X and GX are both racers with incredibly high skill ceilings. Which one is harder depends on what you're doing with the game. I'd argue GX has harder base gameplay, but X has harder speedruns.

I'll also mention Final Fantasy IV because it's shockingly difficult compared to the rest of the series. This one gave me a more game over screens than any of the others.

Iwbtg and all its successors and fan projects

Counter Strike, Starcraft, Dota, Tetris (yes, really), each at the highest competitive level - going by skill ceiling.

Edit: Modern Tetris at the highest level looks absolutely inhuman. I have seen Triple T-Spins at absurd speeds.

Edit 2: You are pretty much physically unable to compete in these games by age 30 at the highest level.

The hardest one I can say I'm honestly proud I figured out are the old "Impossible Mission" games from Epyx.

They have set rules, and once you figure out all the rules, they are solvable, but the platforming elements require precision and the puzzle elements are challenging.

8-bit Souls-Like?

Longplay - 1:

https://youtu.be/ivHFP3dJAkM

Longplay 2:

https://youtu.be/O2AEuLjwBrg

Dark souls, Bloodborne

Crypt of the NecroDancer.

There are three big challenge characters in the base game:

• Aria can only use the starting dagger, no other weapons. She has only one hit point. And she dies if the player ever misses a beat.
• Monk dies if he picks up gold. All enemies drop gold, even ones that normally wouldn't, which turns the game into a routing puzzle where you must never step on squares that an enemy previously died on.
• Bolt plays the whole game at double tempo.

Once you have beaten these three challenge characters, plus the other six easier ones, your next task is All Chars Mode. Beat the game nine times in a row, once with each character. If you die, you must start the whole marathon over.

Beating that unlocks the tenth character, Coda. Coda combines the restrictions of Aria, Monk, and Bolt all at once.

And if you can do that, the final achievement is Lowest of the Low, which requires you to beat All Chars Mode without collecting any items.

The DLC adds a few more hard characters, and another achievement for an extended 13 Character Mode, but they aren't considered to be as hard as Coda or Lowest of the Low. A single digit number of players have stacked the challenges for Coda low% and 13chars low%.

I’m gonna say Jet Force Gemini. It’s not hard in that enemies or bosses are difficult, though some were. It was those damn Tribals. You had to save every single one of them if you wanted to beat the game, and some were a pain to save without them getting killed.

Probably "Trap Adventure 2".
Imagine an old Mario game where Bowser has the most rediculous traps set up. You need to memorize all of the trap locations as well as have the coordination to tip-toe around them to survive.

https://www.youtube.com/watch?v=_nW9k6k1I3k

Army Moves, Navy Moves, or any other old Dynamic Software game. You'd have to be very skilled to get out of the first stage.

Last Battle on the Sega Megadrive (Genesis). I believe there's a handful of people who beat it, but it's genuinely impossible for mere mortals.

And then there's Spelunky 2

Seventh Cross Evolution for Dreamcast... It's just so cryptic and I honestly don't think the developers even know how it works.

Some insane individuals have attempted to speed run it and it still doesn't really make much sense.

EU4...

I like most other Paradox games and I'm at least decent in them I'd say but EU4 just eludes me.