Double Dragon on the original NES. Three lives, no 1-Ups, no continues and no way to recharge your energy during a stage. The best code the Game Genie gave this game was upping the lives to nine. The last stage starts with blocks poking out of the wall and causing major damage. (A Nintendo Power cheat said you can walk by unscathed by waiting for one particular block to punch out twice in a row, but you'll drain the timer doing that!) In the final battle, you must battle two of every foe you faced previously before taking on the TWO Big Bads. Get killed by any of them and you have to face all of them again.
Definitely unforgiving of mistakes, but it is possible to get to the end without cheat codes. (BTW, you can tweak the 9-lives code to give you over 100 lives.) Willy is a sucker for hair pull kicks, and even the last boss is more tedious than deadly (you actually stand a greater risk of running out of time than getting killed). The problem was those friggin' sliding blocks. Pure, sick, disgusting, revolting, stinking, vile dumb luck getting through there in good shape. You can get to that point with 3 lives and get run down to nothing inside of 20 seconds.
If you have the patience to exploit the level-up feature long enough (you gain experience with every hit and while there's a limited number of enemies, they won't die until you hit them with an attack that knocks them down), you can get all your techniques in the first level, making the game noticeably easier. Until you get to the sliding blocks.
The arcade version of the second game. The Elbow Punch has been nerfed so you can't elbow-spam your way through the game like the first. And the enemies are bigger, badder, and attack in greater numbers. And there are no 1-ups this time. Plus, if you're used to the separate punch and kick buttons of the first game, the directional attack buttons in this game can throw you off.
Double Dragon 3 for NES. Take everything mentioned above, add much tougher enemy AI, and cut the lives down to ONE. Yeah, it's hard.
Double Dragon Advance. Too little continues for the spiked up challenge ahead, enemies that can easily hit stun the player every time usually leading into a combo, Mission4, and being considered so difficult that the later released Japanese version is much easier than the American version.
The Adventures of Batman & Robin had many ports with subtle differences between them, mainly involving the boss fights. The actual beat-em-up segments are endless, swarming with enemies, and stingy with power-ups. Punishing on two players, impossible in single-player.
God Hand. A modern heir to the title of Nintendo Hard. Yes, you have unlimited continues, but this is because you will need them. Starting with the very first stage, the enemies will hand you your own ass—repeatedly. Oh yeah, and staying in good condition is completely luck based because you rely on random drops, and oftentimes overpowered demons will just pop up because no reason.
To illustrate: you can use up at least 20 continues on one level, and still be rewarded bonus points. This means they expected you to die more.
To make matters worse, when you do well, you don't level up. The enemies do. Once they've beaten your ass enough, though, it does go back to being easy (if you can call it that).
Lastly, there's Hard mode — You are on constant LEVEL DIE and every Mookwill kick your ass. Heck, Gene claims that you got quite the pair for choosing such a thing.
Mazinger Z: A game based on that Humongous MechaAnime series was released for the SNES. Long stages. One single life. Very sparse recovery items. No 1-Ups. No continues. No password system. No save system. If you die, you have to start again from the beginning. Get fun.
Astro Boy: Omega Factor has three difficulty levels: Easy, Normal, and Hard. Hard mode truly lives up to its name, and if for some reason that's not enough, there's Rebirth Mode, which is ridiculous on any difficulty.
Most games in the Senran Kagura series keep themselves fairly easy with a few spikes in difficulty to add flavor. Senran Kagura 2: Deep Crimson, on the other hand, will often have you begging for mercy as soon as the second mission. This has caused a split between fans who like the challenge, and those who feel it's too hard.
Streets of Rage 3. The American release is merciless, with enemies doing insane damage. You can easily get killed by the weakest mooks if you're not paying much attention, and the bosses have millions of health bars (well not really, but like 7). American mode Normal is Japanese's version of Hard as well, so American Hard is Japanese's Very Hard, which has loads of enemies (easy in Japanese version due to aforementioned weak hits). Anyway, you WILL be spamming those special moves whether it cuts health or not, as if you don't, You're screwed.
Streets of Rage 2 has the secret "Mania" difficulty level, where every single boss has five full bars of health, even basic mooks will out-priority your attacks and have 3/4 of a full life bar, with rarer enemies sometimes having 2 1/2 - 3 bars of health. While the attack damages remain the same, they have ridiculously fast speed and can overwhelm you in seconds. You will need to set your lives to nine (also unlocked by the same code) or you probably won't even make it past the first stage unless you're a Beat-Em-Up god, or doing a Tool-Assisted Speedrun.
Xenophage Alien Bloodsport. Egad! If you're used to beating the computer nine games out of ten on the hardest difficulty in One Must Fall, you're in for a nasty surprise when you try Xenophage. Everything about the computer's behaviour makes it difficult, the special moves are practically useless and the final boss has two forms which you have to beat in one round. On the up side, you do have interesting-looking characters to fight and fight with. Still, don't say you weren't warned when the computer hands you your arse.
Tiny Toon Adventures: Scary Dreams/Buster's Bad Dream. You can't recover health, large groups of enemies with lots of health and hard to avoid attacks, long levels AND you have to start the levels all over again from the beginning if you die... there is a reason why you have unlimited continues. Don't even get me started on hard mode (Easy is already hard enough as it is!)...
Mortal Kombat Mythologies: Sub-Zero: Earth God and Prison Warden/Giant. These guys guard, most likely impossible to defeat due to the awkward control style, especially if you played Mortal Kombat Trilogy first before moving to this game. Even though the key to win them is the Move slide, but the awkward controls makes the two bosses impossible. Playing on Medium or above doesn't even help the condition...
Asura's Wrath. On easy, you pretty much can never die. On normal, it's a bit easy still, but there are some challenges. Hard mode is even harder, but it's still possible - just challenging- to get A ranks and S ranks. What really sends the game into this territory is equipping the Mortal Gauge. Good, God. Even on easy, the bosses are capable of killing you in one hit, and it only gets harder the higher your difficulty is, capable of making every boss in the game That One Boss.
Executioners: The game is this trope for a number of reasons. First, you have Goddamned Bats with most of the enemies, and the big, muscular Elite Mooks can qualify as Demonic Spiders. Second, there is a certain degree of Trial-and-Error Gameplay, especially when you have to position yourself so you don't get hit by the boss's Dynamic Entry at the end of some levels. Third, you have 6 lives, and a limited number of continues, like maybe 10. There is no way to adjust the difficulty. Finally, the game has stiff, clunky, and perhaps somewhat unresponsive controls. But then, this was the first game to be sold by two high-school students named Ethan Petty and Icer Addis, so Nintendo Hard is probably to be expected!
There are two huge stumbling blocks: 1. Being too aggressive in the driving stages and losing all your lives (if you lose one life to time in each, that's fantastic) and 2. Dying in stage 7, thus losing your whip and bulletproof vest; stage 8 is nearly impossible to win without them. Strangely enough, if you do retain them, that stage is pretty easy, and the last stage is more tedious than anything. You CAN beat the final bosses without taking any damage if you have a whip (although it'll take forever).
Weaponlord has a few issues that make it very hard. The most problematic of these is the fact that the controls the controls are incredibly unintuitive at times and very hard to pull off reliably in others. The second major stumbling block is the very overbearing AI in the SNES version (The Genesis version tones this down quite a bit), which is made worse with the already problematic controls. However, to the game's credit, the AI isn't nearly as cheap as it could be in other fighting games, making some of the beatings a bit more enjoyable.
Batman Returns for the SNES. A lot of attacks do absurd amounts of damage, and since Batman has no Mercy Invincibility when he gets up, enemies can and will camp out around his prone body, waiting for him to get up so they can get in a free hit, or even just smack him back down again. The bosses are 'especially'' brutal, able to completely destroy your health in a matter of seconds (Catwoman's dash attack, in particular, can easily wipe you out in only two hits, and is extremely hard to dodge.)
Ninja Combat is hard for all the wrong reasons. Hit detection on projectiles is wonky, but on the other hand trying to actually engage in melee combat is an exercise in assisted suicide, because most melee enemies will annihilate you in one or two hits. It's not uncommon to burn through 2-3 credits in less than a minute from the sheer numbers of melee enemies flooding the screen and dogpiling you to death. You get other characters you can play as as you progress through the game, but all of them pale in comparison to the pair of identical ninjas you start out with (and the last one you get, who only gets short-range projectiles but excels in melee combat, is the worst in the game.)