A good video game boss is a challenging thing. For the developers as much as the players. A good boss has to make defeating it feel like it took genuine effort and mastery to achieve the victory. But it also can't be so simple that the players just breeze through it with no trouble at all. Not too easy, not too hard. And that's not getting into how difficult it is to make a final boss feel satisfying. Gamers can probably think of a few bosses that fit that description. Memorable encounters that made the triumph of winning all the sweeter.

But then there are the bosses so hard that gamers threw their controllers against the wall in frustration. This list is made up of those bosses. These are the hardest of the hard, the biggest challenges any gamer could come across. Some of them are optional, some of them are the final boss, and some are just particularly annoying speed bumps. The one thing all these bosses have in common is their difficulty. That balance described above is nowhere to be found with these guys. They were designed to make players suffer.

We've dug through the history of gaming, from the arcades to the modern day, to put this list together. There are classics and a few more obscure entries. Any gamer that can run this gauntlet is a true master. Dare you take on the challenge?

These are 25 Bosses So Hard We Have To Turn It Down To Casual Mode.

25 Ornstein & Smough (Dark Souls)

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In all honesty, we probably could have filled this list with Dark Souls bosses and called it a day. But if we have to pick one, might as well go with the first game's final bosses. Dragonslayer Ornstein and Executioner Smough. This is a brutal battle with both attacking players at once. If you manage to dodge Smough's hammer, Ornstein will zap you with gold beams. Beating one is hard enough, but then the other will eat his fallen compatriot and grow giant, restoring all his health. The rewards are great but darn if the challenge doesn't seem worth it.

24 Sephiroth (Kingdom Hearts)

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The fight against Sephiroth in Final Fantasy 7 was hard enough, but Square decided to make him even more difficult in their Disney series. If players haven't maxed out their health bar, don't even think about trying to take Sephiroth on. He's faster than lighting and armed with a one-hit KO. Even at max health, he'll take down most players with just three strikes. The white-haired pretty boy's absurdly long katana isn't just for show either. It greatly increases the range of his attacks. And if that weren't hard enough, he actually gets stronger the more damage you do to him.

23 Vergil (Devil May Cry 3)

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Devil May Cry loves to go over the top and nowhere is that more clear than in this final brother on brother battle. Sparks fly every time Dante and Vergil's swords clash, but that's just window dressing for this incredibly hard fight. Vergil constantly regenerates health unless players keep on the offensive.

Slowly chipping away at his health.

That's easier said than done though, as you have to dodge Vergil's own attacks at the same time. Each blow of his will wipe a good chunk out of your life bar. It's a crazy frenetic pace to maintain and claim victory.

22 Senator Armstrong (Metal Gear Rising: Revengeance)

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Leave it to a Metal Gear game to make one of its hardest bosses a pudgy US senator. The biggest surprise with Armstrong though is that he comes after what most people thought was the final boss. But after Raiden takes down another mecha tank, here comes Armstrong buffed out with nano machines. Strategy-wise he doesn't have much going on. It's just each of his attacks deals huge amounts of damage and are wicked hard to dodge. It's a significant upgrade in difficulty from the game's other bosses, catching players just as offguard as Armstrong himself. Remember to vote kids.

21 Ba'al (Diablo 2)

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The final boss of the expansion Lords of Destruction, Ba'al seems to want to wear players down through sheer exhaustion. Before you can lay a finger on the demon himself, you've got to fight through five waves of the toughest enemies in the game. Then if you get through that intact, Ba'al will knock you on your butt. He's got a teleport spell that will frequently blindside you, and his mana drain will draw the battle out even longer. Oh, if you die, which you likely will, you have to fight through those five waves of monsters again. Damnation indeed.

20 Ultimate Alma (Ninja Gaiden Sigma)

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Speed is the name of the game when it comes to Ultimate Alma. For both her and the player. One missed dodge will spell doom for anyone handling Ryu Hayabusa in this fight. If you can avoid her attacks, you then have the difficult task of actually pinning Alma down.

She's constantly shooting projectiles all the while.

Alma will also summon helper demons almost as fast as her to divide players' attention during the battle. And just to add another complication, she's a damage sponge. With all that's happening on screen, your brain might shut down before you beat Alma.

19 Mike Tyson (Mike Tyson's Punch-Out!!)

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The real Mike Tyson went undefeated for a long time. It makes sense his video game counterpart would be just as hard to beat. This final boss battle from the classic Nintendo boxing game is almost like a real match. If you haven't studied Tyson's moves, you've lost already. Players have to have a keen eye for Iron Mike's tells to know what punch he'll throw next. To know when to dodge and when they'll get an opening. If they don't, Tyson's punches will knock them out flat. His uppercut is often a one-hit KO. Nintendo put his name in the title for a reason.

18 Ruby & Emerald Weapons (Final Fantasy 7)

It's a good thing these bosses are optional. Most players wouldn't have finished the game otherwise. They've both got over 1 million hit points and even at level 99, their hits destroy your health bar. And if that absurd number of hit points wasn't enough, these weapons have other conditions too. Ruby can't be harmed by physical attacks, only magic. But it's also got a move which will end your best caster instantly. And Emerald is at the bottom of the ocean, forcing you to beat it before you run out of air. It's like they're designed not to be beaten.

17 Yellow Devil (Mega Man)

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This blob monster is creepy enough without being impossible to defeat. This may the simplest boss battle on the list, but that doesn't make it any easier. The Yellow Devil will fire a projectile at you, then split into blobs and fly across the screen.

You've got to dodge all of it perfectly.

This is made harder because the Yellow Devil is a giant twice the size of Mega Man. His flying blobs cover most of the screen. Once he reforms, you'll get the slimmest of chances to hit him. Easy to learn, difficult to master. Just like Mega Man.

16 C'Thun (World of Warcraft)

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Here's one boss so difficult, the developers actually had to tone it down themselves. Before he was patched, C'Thun could take out whole raiding parties alone and treat individual players like nothing. His attacks turned into massacres. C'Thun would swallow players whole. His eye beams would disintegrate anyone in their path with a one-hit KO. And his tentacles could wipe out parties of 40 or more. In the 45 seconds, he was vulnerable, players would be lucky to deal any damage to his health. Blizzard stepped in eventually and nerved C'Thun, but his difficulty had already passed into World of Warcraft legend.

15 "Through the Fire And Flames" (Guitar Hero 3: Legends of Rock)

A Level In Guitar Hero 3
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Guitar Hero 3 Gameplay

Some people's fingers just started bleeding from reading that. Even on easy mode this song will kick your teeth in. It doesn't ease you into the rhythm, no, it drops in you in at full speed and expects you to keep up.

For all eight minutes of the song.

With the amount of precision, dexterity, and hand-eye coordination needed to pull this off, you could probably play this song on an actual guitar. Seriously, if anyone tells you they got 100 percent on "Through the Fire and Flames", you hand them a bar of soap. Because they're a liar.

14 Psycho Mantis (Metal Gear Solid)

9- Psycho Mantis
Via: Attack Of The Fanboy

The encounter with Psycho Mantis certainly takes the prize for weirdest boss battle on this list. Thanks to his psychic powers, He'll break through the fourth wall and taunt you. You, as in the player. Psycho Mantis will read your Playstation's memory card and make your control shake through the rumble feature. That's crazy enough, but he was also able to predict every move you'd make and avoid as much damage as possible. The only way around this? Plug your controller into another port. Seriously. A bizarre fourth wall-breaking trick to beat a bizarre forth-wall breaking boss.That's like sixteen walls!

13 Bowser (Super Mario 64)

Super Mario 64 Bowser
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Come on, you know Bowser had to be on here. Why Mario 64 though? Well, it was the first time gamers battled the Koopa King in 3D. That added a whole dimension to the challenge. In essence, this another simple yet difficult boss fight. You've got to grab Bowser by the tail and swing him off the platform. But he's harder to pin down then he seems. You've got to be careful with your aim too, otherwise you may not land a winning blow. Though this boss battle isn't as difficult now, it's still a classic. You gotta respect the classics.

12 General Raam (Gears Of War)

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No boss on this list will put you on the defensive faster than General Raam. The final boss of the original Gears of War, he's still a challenge even all these years later. His mini-gun is a one-hit KO, he's got a Kryll shield that also attacks you, and he's got Reavers working with him.

A shame your AI partner won't be much help.

This fight is all about cover and taking your shots where you can. Going head-on will get you fragged instantly. There is always a co-op mode. But a solo victory will be all the sweeter.

11 Lady Comstock's Ghost (BioShock Infinite)

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Okay, so Lady Comstock's Ghost herself is not the most difficult boss in the gaming world. But the way to make her vulnerable will have you pulling your hair out. Lady Comstock will summon zombie soldiers to swarm you. Beating all of them forces her to re-summon them, leaving her open for a brief window. And we mean very brief. Better be sure to save some of your ammo for that opening too, or you'll have few ways to take advantage of it. This has to be done three times as well. You ain't afraid of no ghost.

10 The Ender Dragon (Minecraft)

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Yes, Minecraft does actually have boss battles. And the Ender Dragon is more than difficult enough to make this list. It's got most of the things the others here do. Massive damage-dealing blows, a deep health pool that regenerates, support minions. But the Ender Dragon's true difficulty lies in how much stuff you have to craft to fight it. You'll need enchanted armor, potions, food, Ender Pearls and to build an End Portal. That portal is one way too, so if you lose or all your supplies break, you have to start all over again. Maybe stick to house building.

9 Sinistar (Sinistar)

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"Beware, I live." Those are the words that will greet anyone foolish enough to try this arcade classic. Sinistar himself is challenging enough. Like many bosses of his era, simply touching him means instant ending for the player. But Sinistar will also chase you relentlessly, threatening to suck you into his gaping maw.

He hungers.

He also shoots asteroids and projectiles at you the entire time. But the most unnerving thing about Sinistar is that he constantly taunts you before he even appears. His evil gravelly voice bellowing from the speakers about his hunger. It'll get in your head man.

8 Kai Leng (Mass Effect 3)

Via: ign.com

Ninjas are a bloody nuisance aren't they? Even in the sci-fi world of Mass Effect they're making trouble for people. Kai Leng certainly annoyed plenty of players of Mass Effect 3. His lightning-fast attacks shook up the rhythm of an otherwise cover-based shooting combat style and dealt huge damage along the way. His strong shields and AI soldiers only added to the difficulty. They are just distractions to get players to waste their ammo. Like most bosses on this list, you need to think strategically to defeat Kai Leng. Well, that and deal with the lack of cover to shoot from.

7 Shao Khan (Mortal Kombat)

Shao Khan Vs Liu Kang
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Shao Khan is so hard to beat, it's not even funny. In some Mortal Kombat games he's straight up broken. Back in the Sega Genesis days, he blocked attacks like it was nobody's business and taunted players mid-fight. Plus his attacks, which included a gosh-dang sledgehammer, kept players on the defensive for most of the fight. Whether it was close-up or far away, Shao Khan always had a trick up his sleeve (or lack thereof) to keep his opponents from getting any kind of hit in. It says something about a fighter when your only opening is him mocking you.

6 Giygas (EarthBound)

via: legendsoflocalization.com

Thank heaven this game originally came with a strategy guide. Otherwise, many people would have gotten stumped by this absolute monster of a final boss. Like many JRPG bosses, the fight against Giygas takes on several phases.

In some of them, he's outright invincible.

It's only when you learn to use an ability that was useless in the game up until now that you hurt Giygas at all. And you have to do it nine times! But in addition to that, Giygas is just creepy. EarthBound never makes clear what exactly he is and his onscreen avatar is demonic as heck.