[[VideoGame/MegaMan2 http://static.tvtropes.org/pmwiki/pub/images/airman_taosenai_nekokan.jpg]]
[[caption-width:260:You'll wish you just had to fight Air Man after dealing with these guys.]]

Mega Man stands as a shining example of classic NintendoHard. These guys are the reason why. It doesn't matter if you've got the [[GoodBadBugs Time Barrage glitch]] or a [[VideoGame/MegaManBattleNetwork folder full]] of [[LimitBreak Program advances]], these mechanized murder Masters are coming for you.

Please keep in mind that if there's an easy method to take out a boss, they're not this trope. Remember as well that WeAreNotGameFaqs, your example shouldn't read, "Unless you do..." or "But if you have..." If there is a trick to defeating the boss, it's probably not an example in the first place. This being Mega Man, every boss has a weapon that they're weak to. If that weapon turns out to be impossibly frustrating to use, that boss probably belongs here.

BonusBoss is now banned from being ThatOneBoss. It's optional and you know it's overpowered, nothing prevents you from not fighting it.



[[folder: ''Mega Man'' (Classic series)]]

* Fire Man, mainly because his fire pillar attack is very powerful and you have to have ''perfect'' timing to jump over it. He also frequently uses this move as well as his regular Fire Storm like there's no tomorrow, so even having the Ice Slasher isn't going to guarantee you victory.
* The Yellow Devil from Wily Stage 1. As lamented in [[http://www.youtube.com/watch?v=hN-YHyDrCdc& this song]], many gamers have lost a good chunk of their childhood trying to get past this shining example of NintendoHard. Unless they cheated.
** The Yellow Devil's difficulty stems from his attack pattern; he splits apart and flies across the room one piece at a time, and you have to have crazy good reflexes to dodge him without getting hit. Once he's fully formed, his eye opens and fires a fast-moving projectile at you, then it closes and he starts flying across the room again. You only get a couple of seconds before the eye closes, and if you're trying to kill him with the Buster, the eye sometimes opens too high to hit. Not only that, but he takes forever and a day to die.
** The worst part about the Gamecube version ''Anniversary Collection'' is that the glitch that makes the Yellow Devil easy to beat was drastically changed (the timing was changed to make it less effective if you knew the change, worthless if you didn't), thereby making the fight that much more difficult.

* If you don't have his weaknesses, then Wood Man is a hassle to defeat. He hits hard, and he is also one of the more durable Robot Masters. His hardest attack to dodge is his leaf shield which requires a well-timed jump to dodge. You also have to worry about his swirling leaves, which require good dodge maneuvers to get through. And what's worse is he advances towards after each attack, forcing you to run under him (good luck not getting hit by him as you do this) to the other side while dodging his leaves as they descend. Yeah... don't fight Wood Man first.
* Air Man is an interesting example. Due to [[EarWorm a certain song]], he has been elevated to MemeticBadass status, despite being only moderately difficult. The context of the song lost in translation was that it was about a player who never played games trying out Rockman 2. Modern Western fans are left scratching their heads, [[MemeticMutation but the meme just stuck around]].
** The main problem with Air Man is that he can [[RandomNumberGod sometimes]] throw out his tornadoes in patterns that require extremely precise jumps to dodge. To a normal player this isn't so bad, as it's not too difficult to damage Air Man faster than he damages you, [[LuckBasedMission but trying to do a]] NoDamageRun...
* Quick Man, and not just because his stage is [[ThatOneLevel a pain to beat]]. He is incredibly fast, and takes out almost 4 units of your life bar via contact. While Flash Man's Time Stopper can take half his life in one shot, the player will probably need it to get past the daunting laser barrage right before his door.
* The Mecha Dragon in the first Wily Fortress stage. Someone even wrote a blog entry in which this boss fight was compared with a major real-life hangup. Made harder in ''Anniversary Collection'', which removed [[GoodBadBugs an exploitable bug]] to make yourself invincible during the fight.
* The Buebeam Trap, the turrets with blindingly fast shots from the walls heading straight for you every five seconds or so. It's one of two bosses in the Wily Castle that only has one way to damage it, the Crash Bomber. And the kicker? You only have seven uses of the weapon maximum. Five to actually destroy the turrets, and both of your remaining shots to break barriers blocking the others. To make matters worse, there are plenty of other doors you can bomb to 'make your life easier'. This is a cruel beginner's trap, as there is no way to win if you use just one bomb incorrectly. If you don't make clever use of Items and/or accidentally miss a shot then [[UnwinnableByDesign you will not be able to defeat this boss]]. And since you don't get energy refills after death you either need to take forever restocking energy off the few enemies or just game over entirely and restart the stage. There's a reason why practically every ''VideoGame/MegaMan2'' ROM hack out there, even the obscenely hard ones, generally make this boss ''easier''.
** The only mercy you're given is that the barriers you destroy don't respawn. Unless you game over. Small mercy, because, as previously mentioned, now you need to grind up all your crash bomb ammo from the Demonic Spiders of this game.

* The Doc Robot takes the abilities of ALL the Robot Masters from ''2'' (You fight two per level, and they make you play through the four harder stages revamped to be harder). If you thought dodging Wood Man's swirling leaves was bad before, try it when they are even larger! Try fighting Crash Man without an attack that can shoot up! TRY FIGHTING A LARGER, FASTER QUICK MAN!
** Oh, and since it's ''VideoGame/MegaMan3'', you now have to try and figure out which weapons the ''VideoGames/MegaMan2'' robots are weak against, all over again. Almost none of them are intuitive either. Even when you ''do'' figure out their weakness, they aren't as effective as their weakness was in ''VideoGame/MegaMan2'' (nothing can break through the Leaf Shield, for example).
* Doc Wood Man, as the Leaf Shield has both larger leaves and larger shield radius -- large enough that you almost need Rush Coil to get over it (which consequently smacks you into the leaves coming from above).
* Doc Heat Man who, just like Shadow Man, is vulnerable to the Top Spin, and it's very easy to use up the weapon energy for it without defeating Heat Man if you're not lucky.
* Doc Air Man is weak against Magnet Missile and Spark Shock, two weapons that are not quite effective at actually hitting him. If you die against him, you have to start the entire stage over, as opposed to getting dropped in the previous room like the other robots.
* [[ConfusionFu The Doc Robot mimicking Quick Man.]] Remember how in 2, Quick Man was a FragileSpeedster and STILL tricky to beat? [[LightningBruiser Remove the fragility and increase his size]] [[OhCrap and you have this boss.]]
* Flash Man's simplistic pattern in 2 made him a pushover. However, the same can't be said for Doc Flash, as small changes made this pattern an actual challenge. He's taller than Flash Man, so it's difficult to jump over him without getting hit. He uses Time Stopper more often and the SpreadShot that he fires during Time Stopper covers a much larger radius than Flash Man's. And if you're not careful, pressing the Shot button while getting hit by the Spread Shot will ''cancel your MercyInvincibility and you'll get hit again''! Oh, and like the other Doc Robots, he hits harder and has more durability. Luckily, Doc Flash doesn't jump after getting hit like Flash Man did, which would have made this already difficult battle even more challenging.
* Shadow Man. He is insanely fast, and his attacks are very hard to dodge. On top of this, the only weapon that can hit Shadow Man effectively, the [[ScrappyWeapon Top Spin]], has to be used at very close range, and its weapon reserve energy drops like a stone when you are using it while in direct contact with Shadow Man. What tends to happen is that if you try attacking directly with Top Spin, ALL of its weapon power can get drained when you land your first hit. Then Shadow Man still has 75% health and you have no Top Spin power left. Good luck hitting him with the Arm Cannon, and even if you know his pattern, he is still very difficult to beat.
* Dr. Wily has a second incarnation of the infamous Yellow Devil, the Yellow Devil MK-II, waiting for you in the second stage of his castle. This Devil boss is, however, considerably easier since it's normal attack isn't as fast as its predecessor (and the blocks come at you closer to one-at-a-time intervals), and you have sliding and E-tanks. Good luck getting through its "bounce across the room in pieces" attack without getting hit though.
** But if you are a hardcore ''Mega Man'' gamer who believes using E-Tanks at any point in a game is sacrilege, then this Yellow Devil is harder than the one in ''VideoGame/MegaMan1'' because of the attack that was just pointed out.
* Needle Man is also pretty bad, especially if you're trying to do a No-Damage Run. His attacks are unpredictable, he has a long-range attack where he impales you with his head, and he will fire out spikes at a machine gun rate that are really hard to dodge. He's also pretty durable, unlike Quick Man.

* Bright Man, who's basically a much tougher version of Flash Man from ''VideoGame/MegaMan2''. Flash Man just randomly ran around and occasionally froze you in place so he could hit you, but Bright Man does the same thing with a much higher AI and much more jumping around, timing it so when you try to dodge him he'll freeze you and then attack. Fighting Bright Man becomes less of a task if you shoot him with the Mega Buster once and then use his weakness, Toad Man's Rain Flush, as he will never use his Flash Stopper from that point on [[spoiler:because he will only use it when his health is at exactly 16, 8, or 4]]. Even if you figure out his pattern, he is still a major pain, especially for those people out doing {{No Damage Run}}s.
* Dive Man, mainly because he's quick and aggressive, and the one weapon that does any real damage to him is the [[ScrappyWeapon Skull Barrier]], which is so small that colliding into him with it pretty much means you're going to take ''huge'' damage in the process. It doesn't help that Skull Barrier disappears if ''any'' projectile touches it. Dive Man's weapon is also a homing missile. Since you can only afford one or two mistakes using Skull Barrier, you basically can't do anything until you know you have a clean shot at Dive Man. [[ViolationOfCommonSense You essentially have to be close to an enemy that wants to ram into you]].
* The second phase of Wily Machine Number 4 is absolutely brutal if you don't realize you can [[spoiler: pre-detonate the Drill Bomb and explode it to hit Wily's weak spot: any other weapon (save for the Mega Buster) either does little to no damage and if you don't detonate the drill before it hits the weak spot, it'll just bounce off]]. He fires a constant barrage of huge fireballs bigger than Mega Man with no discernible pattern. And yes, the weak spot on his machine is just a bit too high to reach with a straight shot at your apex. Pharaoh Shot which can be aimed upwards, doesn't work. If you don't know how to use Drill Bomb properly, you're going to have to self-terminate on that level over and over until you've stockpiled all 9 energy tanks if you want to win.
* Pharaoh Man is often called the Quick Man of the game, and he earned it. He jumps around the arena while throwing small Pharaoh Shots at you, and then he stops to charge up a powerful Pharaoh Wave, and while dodging Pharaoh Wave is not bad if he does it from the lowest or highest areas of his arena, the rematch in Wily Castle takes place on a flat arena, so good luck timing your jump over it.
* Ring Man, mostly because of his massive CollisionDamage, dealing eight units of damage if he collides into you. He also has an erratic and unpredictable AI pattern, and if you think you can stay on the ground to attack him, he'll immediately counterattack you.

* Charge Man. His charge attack can catch the player off guard if not careful, and he spends most of the battle in an invulnerable state (again, either from charging Mega Man or using his coal attack). Good luck using his weakness, the [[ScrappyWeapon Power Stone]].
* Gravity Man. The fight against him is purely disorienting, and the switch in controls can often take your slide out of the equation for the most part. Hitting him with anything can be difficult because of how tiny a window you have to do so, this combined with the fact that his shots tend to be uncannily accurate. He also has a nasty tendency of shooting your Star Crash to cancel it out right before switching the gravity, therefore removing your opportunity to hit him ''and'' wasting the weapon's energy.
* Dark Man 1 simply moves slowly and stops to shoot often and upon taking damage. However, upon taking a certain amount of damage, he will move faster, and become more difficult to avoid. His weakness, the Water Wave, only has 14 uses, so it is likely that dying to him will mean players will end up fighting him with little or no uses of it left.
* Dark Man 3 fires three rings that immobilize Mega Man completely, allowing him to hit him easily (which will pretty much always happen). They're difficult to dodge at a close range as well. His major weakness, Beat, is a weapon that can only be found by collecting all the plates that spell "MEGAMANV" in the Robot Master stages and thus some players may not have. In addition, the boss after Dark Man 3 is also weak to Beat, and the stage containing it is short with absolutely no way to refill weapon energy, so players that DO have Beat will want to save it for him.

* The dinosaur robot boss Mechazaurus has a [[GoForTheEye weak spot]] the size of a pinhead that can only be reached by riding the flying platforms that emerge from its chest, and said weak spot is picky about what counts as a hit and what doesn't. It also periodically spits fire blasts with deadly precision, which is highly likely to hit you while trying to ride the platforms up, and if a flame hits the floor it lingers there for a second. Its weakness (the Yamato Spear) is fairly limited in uses, so it's possible to run out of it because they didn't count as hits.

* Freeze Man, with his extremely erratic, hard-to-predict pattern, swift movement, fast attacks coming from every angle, and ability to immobilize you? Yeah, that.
* Slash Man, who's fast, strong, and can immobilize you with a red adhesive-like substance. It doesn't help that it's also really hard to hit him with his weakness weapon because he's always jumping around the room.
* [[AdvancingBossOfDoom HannyaNED]], the flying oni mask boss at the end of Wily Stage 3. The screen autoscrolls, it has a plethora of hard-to-avoid attacks such as barrages of bombs and EyeBeams, and its weak point is very small and can only be reached by jumping on the missiles that only stay on screen for a fraction of a second.
* The Wily Capsule 7 also fits here. He is definitely overly hard by the standards of final bosses for the ''Mega Man'' series. His weakness, the Wild Coil, is (as per the tradition) difficult to hit him with. His main attack is shooting four elementally charged orbs in your direction, then [[{{Roboteching}} they stop in mid-flight to adjust their path]]. The ice sphere hurts less, but freeze Mega Man in place, while the fire sphere is as powerful as Turbo Man's Scorch Wheel. Fortunately, he's at least damaged by some other, easier to hit with weapons, such as Freeze Cracker. WordOfGod says that even the developers found this one impossible without E-Tank usage. Even has some LampshadeHanging, in which Mega Man attempts to kill Dr. Wily following the battle.
** This battle is ''so'' bad that the creators actually used it again as the final battle in ''VideoGame/MegaMan8'' and significantly lowered the difficulty. When a final boss battle is so tough that the programmers actually redo it in the next game just to apologize to fans that struggled getting through it initially, it ''definitely'' qualifies for ThatOneBoss.
** You know the boss fight is ridiculous when a common bit of advice for fighting him is "Just get hit by the yellow orbs. They hurt less."
* The final fight with Bass, when he combines with Treble, can be extremely tough if you don't have the Super Adapter. If you ''do'' have it, the fight is still tough, [[BestBossEver but a lot more awesome.]]

* Astro Man, if you don't know the way to dodge his Astro Crush or use the Homing Sniper to immobilize him on the ground, he will destroy you easily and quickly. Oh yes, and he's also the boss of ThatOneLevel, so have fun with that.
* There's the first Wily Fortress boss, that can only be hit by the Mega Ball, a weapon that has to bounce off of the wall up to the ceiling at the right angle to hit the boss. It doesn't help that its level is pretty tough to get through normally. The biggest reason this counts, though, is because it's a GuideDangIt moment -- if you hold the up direction while kicking the ball, it goes at an upward angle instead of forward. This boss is a whole lot less annoying if you know this trick, but of course that doesn't mean the game ever tells you this.

* Tornado Man, mainly because his attack is ''very'' difficult to dodge if you're not fast enough to avoid and his weakness weapon is a ground based attack and he spends most of the time flying in the air.
* What's worse than one Devil? ''Two of them at the same time''. Both the yellow and green devils sent blocks of each other right at you at the same time. The pattern is actually easier this time, however, but the core flying out to switch blobs in the middle of it all makes it painful. Fortunately, the pause-glitch works on it.
* The Paozo elephants from Concrete Man's stage. What makes it worse is the fact they're ''only mini-bosses''. These guys are also found in the downloadable Special Stage featuring [[spoiler: Fake Man, the impostor police robot who arrested Dr. Light]] and Endless Attack.
* Concrete Man, hits very hard. The Laser Trident doesn't do many damage to him and he has an unavoidable attack if you're stuck in concrete. While the Laser Trident can pierce through the block of his weapon, it don't work if you're trapped in it--and they travel diagonally from the air and are ''very fast''. He's so bad that he can even screw up the BossRush.
* Dr. Wily in this game rivals his ''VideoGame/MegaMan7'' incarnation. A three-form fight with ''no breaks'', and the first has a very unorthodox way of dealing damage. It doesn't help that it's pretty hard to hit Wily Capsule with Plug Balls, as the ball will go straight down when in midair--and he often spawns in midair, meaning you have to be on top of him to hit him.

* Strike Man is one boss who both inverts this and plays this straight depending on the circumstances. He's the easiest Robot Master to beat with his weakness weapon [[GameBreaker the Triple Blade]], but the hardest to beat if you don't. His Rebound Strikers are very fast and he can have multiples of them at once. He's also the boss of a level that has not one, but ''two'' annoying mid-boss fights. Better hope you have his weakness weapon, or a lot of E-Tanks, because if you don't...
* Blade Man is like a powered up Shadow Man from ''VideoGame/MegaMan3''. He's even faster and stronger, with multiple projectile attacks that are tricky to dodge. He can also negate his weakness weapon the Commando Bomb if he swings and hits it before it can detonate right next to him, and the bomb itself does minimal damage, meaning the shock wave from the explosion has to hit Blade Man before he jumps to the ceiling or another wall.
* Pump Man, mainly because he controls the water current on the floor to work against you and make you even slower than you already are, which makes dodging his attacks almost impossible, especially as Mega Man who can't slide in this version. It doesn't help that he can negate his weakness weapon, the Thunder Wool, if he times his attack correctly.
* Solar Man is pretty much impossible without his weakness weapon, the Water Shield, mainly because he can absorb the shots from your Mega Buster and shoot a huge burst of energy right back at you when he has enough power. Good luck if you take him on first, especially since the mini-boss Suzak & Fenix are just as tough.
* The ''Block Devil''. Imagine, if you will, an unholy union between the Pico Pico Master (2nd fortress boss from ''2'') and the Devils' penchant on splitting and reuniting in definite patterns, throwing in a weak point that stays on screen only 1/3 of the battle and ''a bottomless pit'' that becomes a KaizoTrap if you happen to defeat the boss standing on/over a purple block. Its weakness is one of the most awkward weapons in the series, too!

* This game is notorious for Dynamo Man, who likes to hop into a recharging rig in mid-battle. By the time you break it, he'll have regained at least a third of his HP (and he'll happily refill completely if you take long enough).
* Just as bad as Dynamo Man is Burner Man, who resides at the end of ThatOneLevel, and has several attacks that deal a lot of damage as well as one that holds you in place as he has his way with you. His Wave Burner is also capable of deflecting shots, and he likes to back you into a corner with it. Fighting him with his weakness, Cold Man's Ice Wall, he becomes somewhat of a PuzzleBoss, having to use the Wall to push him into the spikes on either side of his arena. Thing is, Ice Wall can be only used when he is on the ground, any other time and he'll bust right through it, and you've wasted your ammo. If you mess up too many times, it's easy to run out of ammo, and be forced to go through his agonizing stage all over again.
* King Plane of the second fortress stage. It's above a bottomless pit, you have to navigate randomly appearing platforms that the boss can destroy, one of his attacks will blind the screen, and is just a pain overall. You will fall into a bottomless pit and die multiple times even if you utilize a few weapons based tricks to stay in the air and/or keep damaging it.

* In ''Mega Man 1'', Cut Man was pretty easy to take down with the default Mega Buster, and a complete joke if you had the Super Arm. In ''this'' game he moves far faster, his Rolling Cutters are even faster still and far more damaging than they were on the NES, and Cut Man's weakness (the Fire Storm) isn't anywhere near as effective as his previous weakness to the Super Arm.

* Crash Man[[note]]Or "Clash Man" as the game calls him[[/note]] stands out in what is otherwise a ludicrously easy game, as he's the only Robot Master to actually be ''harder'' than on the NES. His weakness is still to the Air Shooter, but he takes much less damage and will only be hit by one of the three tornadoes from each shot (all three could hit him in the NES version), meaning even if you hit him with every shot he'll still have about a quarter of his health left. On top of that, you fight him in a much smaller arena than you did on the NES, making it much easier to pick up SplashDamage from his bombs.
* Living up to his MemeticBadass legacy, whilst generally fairly easy to defeat, Air Man in this game has a tornado pattern that is quite literately impossible to dodge. And he has a 1/4 chance of using it every time he fires. Have fun no-damage runners!

* Punk certainly lives up to his Mega Man Killer title. He deals serious amount of damage just like Elec Man and Ice Man. He throws very fast traveling projectiles while jumping, and then he curls up and cannonballs himself to the other side of the room at a breakneck pace, and the height he cannonballs at is done at a varying height, which means you have to slide under or jump over him accordingly. And he ''only takes damage from the Mega Buster and nothing else''. Good luck!

* Bright Man is easily the cheapest Robot Master in the game. Why? Well, remember how in ''Mega Man 4'' he would only use the Flash Stopper when his health was at a certain point? Yeah, that quirk's gone now - he uses it whenever he wants and will seemingly ''always'' abuse it to jump into you while you're completely helpless to avoid it. Put simply, if you walk into his fight with anything less than full health and/or E Tanks, he's already won.

* Uranus is easily the hardest of the game's Stardroid bosses. Not only do his attacks cause ''major'' damage, he has a OneHitKill move that he frequently spams you with, and only Pluto's weapon, the Break Dash is capable of causing him more than a single damage point (even a fully-charged Mega Arm hit does just one point of damage).
* The final boss, Sunstar, has ''no weaknesses'' and three forms, all of which can do major damage to you.

* CWU-01P, especially when playing as [[JokeCharacter Rock/Mega]]. His main way of hurting you is CollisionDamage. Sounds easy, right? WRONG! At least on the aptly-named Hard Mode, he's damned fast. And as the aforementioned JokeCharacter, you can't hurt him without getting right in his face and kicking him enough to first get rid of his bubble shield, then once more to actually cause damage. Oh, and just for good measure, he does also have another attack -- a [[FrickinLaserBeams frickin' laser beam!]]
* Also, if you're playing as a "Boss Character" Robot Master, when you have to fight the Master whose weapon is strong against you, ''good luck''. Your attacks will barely scratch them, and they can inflict a ton of damage on you in turn.
** Special mention must go to fighting Cut Man as Bomb Man, as ''all of his attacks can destroy your bombs''. In other words, the only way to do any damage to him is to throw a bomb behind him and hope that he doesn't jump away before the bomb explodes. Lather, rinse and repeat 15 more times.
** ''Any bosses'' when playing as Oil Man, but ''especially'' Fire Man. He can turn your already-pathetic attacks against you ''hard'' by [[IncendiaryExponent lighting them on fire.]]

!!''Game Gear Megaman''
* Napalm Man, who went from being one of the easiest bosses in Megaman 5, to one of the hardest here, all thanks to a change in AI that makes him very aggressive, and no longer follows a predictable attack pattern what-so-ever. On top of the AI change, everything he fires at you now explodes, rather appropriately, which makes even his first barrage of attacks pretty tough to dodge on such a small screen.

* Vega (Claw). He only uses melee attacks, but he's [[LightningBruiser very fast and does a large amount of damage]], and his weakness is a melee attack. He also has ThatOneAttack where he leaps onto the railing and tries to slash down on you, and is very hard to evade if he performs it in the middle of the arena (hint: slide when he is halfway down to feint him). In fact, the move you ''want'' him to use is his Limit Break, which isn't too difficult to evade and leaves him open in the center after it ends.


[[folder: ''Mega Man X'' series]]
!!''VideoGame/MegaManX1'' / ''VideoGame/MegaManMaverickHunterX''
* The Bospider, due to the speed she moves at, the difficulty of quickly figuring out where the boss will end up depending on what pole she appears on and where the pegs she moves along appear and the timing needed to hit before she regains its invincibility. And then she TurnsRed... Good luck hitting it with its weakness, too. It's not even good against the mini-spiders, since it'll only hit one and the firing rate isn't fast enough to shoot at the one behind it.
* Boomer Kuwanger is an absolute monster without his weakness weapon, mainly because he can easily teleport through your other weapons and counter you with his [[ThatOneAttack Dead Drop]], and his dashing capabilities far exceed yours which means that running from him while dodging his Boomerang Cutter that can hit you while you're wall climbing make for quite a frustrating time. Even most purists who prefer to mainly rely on the X-Buster for the majority of their playthroughs will make a ''big'' exception for this guy, which makes perfect sense considering he's like the Quick Man of this game.
* Armored Armadillo has 3 strategies: guarding, bouncing off the walls and shooting his energy shots. He's invincible when ever he isn't shooting at you, as he will most likely block your attack. Guess what he decides to never do 90% of the time.
** Now try fighting him on ''Maverick Hunter X'''s Hard Mode, where he picks up an attack where he bounces off the walls ''and'' fires off bullets in four directions. Even if you use the Electric Spark to take out his armor, it's still hellish.
** Try fighting Armored Armadillo WITHOUT beating Spark Mandrill[[note]]for added difficulty, receiving Dash Boots from Chill Penguin's stage[[/note]] first. Even a fully charged X-Buster shot won't even scratch him.
* Launch Octopus. He dishes out homing torpedoes like candy and MoreDakka is his trademark. When he's not firing torpedoes at you, he's jumping clear across the arena right on top of you. And to make matters worse, he also has a nasty attack called E-Drain where he creates a whirlpool that pulls X into his grasp. And guess what [[LifeDrain it does when he grabs you]].
** You can cut off his tentacles, making him unable to do Homing Torpedo and E-Drain, but this results in him spamming his straight firing torpedoes. Also since his weakness is stopped by one projectile, you'll have a ball of a time even hurting him.
* Sting Chameleon. One of the few bosses in the game widely considered to be a total death wish for new players, and still a pain for even veterans. The very annoying part about his fight is when he clings to the ceiling to rain the spikes in his room down on you, which fall quite fast, aren't all that easy to dodge, and their damage adds up eventually. On top of that, thanks to his ability to disappear and reappear at will to attack as well as to dodge ''your'' attacks, it turns his battle into a very long, hit-and-run war of attrition. His iron tongue attack is near-instantaneous and does decent damage, and he can take plenty of punishment as well. If you slip up even a bit in this fight, you ''will'' pay for it.
* However, the most difficult boss in the game by far is Sigma. First off, he has three forms, all of which can do massive damage. Assuming you picked up everything in the game, his dog can kill you in 5 hits. However, these collectibles can be monstrous to get, with some making no sense whatsoever. If you miss some heart tanks, you will pay. Notice I haven't gone into the boss itself yet.
** Phase one is hard. The dog has two attacks, which deal loads of damage. The fire attack arcs in a line to do massive damage, while the spark attack is almost a guaranteed hit if you aren't wall-jumping. The second phase has two settings. There is a pattern you can lock Sigma in which makes him easy. However, he will knee you in the face if given a chance. This is a heavily damaging attack. Also, he blocks. Which leads to phase three.
** Only two weapons can hit Wolf-Sigma's head, and both are un-wieldly. A fully charged buster shot, a 5-10 second charge, does 1 damage. The Rolling Shield, the most annoying weapon to use in the game thanks to an inability to fire straight, does two. However, this is just how you damage him. His attacks do anywhere from one 'weak' hit of 5 damage, or 10-14 damage out of your life bar, a 4HKO at most. This is only aggravated by what those attacks are. This boss has two hands and each can do two attacks. They can shoot lightning, which is telegraphed, covers an entire column of the screen, and will be spammed. The hands also swipe at you, which is your one true opportunity to get on them and ride them up to Sigma's head. Unfortunately, you won't have much time. As soon as the hand gets back to its original position before the swipe, it will shoot lightning. There is one other opportunity to get on the hands: wall jumping up the sides and praying that his hands are both out of position and not firing. Sigma's head also has two attacks. It telegraphs when, but not which attack it will use. It can fire electric sparks which take an almost perfectly timed dash to dodge, if you are not in the corner where it starts. It also can breath an impassable stream of fire which can start in the mid-right or mid-left of the room. Since you have no idea which attack Sigma will use, nor where it starts, you have a 1/4th chance of getting hit without a chance to dodge. The lightning from the hands attacks separately, and loves to trap you between fire and lighting. This is the worst fight in the game, bar none. And third in annoyance to the Yellow Devil and Buebeam trap in the entire series.

* If you collect all of Zero's parts from the X-Hunters, then you'll be able to skip the battle against Zero at the end of the game. If you don't, you're in trouble at the end of the game before you battle Sigma. The only weapon that really hurts him-the Speed Burner-is hard to hit him with, and his attacks are hard to dodge and they HURT. And after you've beaten him (probably draining all your Sub-Tanks in the process), you still have to fight Sigma. The moral of the story is to get all of his parts, no matter how hard they are to get early in the game.
** Zero's AI is easily predicted/manipulated and all of his attacks are avoidable. All of which means absolutely nothing, as Zero is just too damn fast. Slipping up AT ALL will have you eating his attacks as he grinds your face into the floor.
* [[LightningBruiser Violen]] is the worst of the three fights you have to do to get the Zero Parts, considering he liked the idea of Armadillo's invincible attacks, but decided to make them even less predictable. Lady Luck needs to be on your side both times to defeat this guy. Why? His ball-and-chain attack. Whenever he fires it, it will do one of two things. Either it will bounce in an arc in a far-mid-close range configuration, or it will bounce around the room at random. When it bounces randomly, it will lazily trail Mega Man, but it bounces off the wall at weird angles. Trying to outrace it is impossible, as it merely has to decide to cut your escape route off and it will.
* Serges is even worse the second time you face him. He's long been held up as the hardest boss of X2. The fight starts with Serges in a tank with four cannons, taking up half the screen. The other half is reserved for you, four platforms that move up and down, and a floor full of spikes.
** In the first half of the fight, Serges will move up and down inside the machine, and fire whatever cannon he is behind when he stops. The projectiles from the cannons bounce and curve oddly, making them hard to predict. In addition, Serges is fast, and you may not realize which projectile he's going to fire before it smacks you in the face. If you decide not to use the Giga Crush (why?), didn't find the upgrade (possible), or don't have it charged (likely), you'll have a lot to balance.
** Once the cannons are destroyed, the second half begins. Serges' tank moves forward, destroying two of your safe platforms. After that, he will constantly fire green shots that split into fours. He has very good aim, and while the split pattern is predictable, it's difficult to keep track of while jumping around on what limited safe space you have. His weakness is the Sonic Slicer, but good luck hitting him with it, since it flies slowly and not quite straight.
* Even the first fights can be challenging without their weaknesses. Serges in particular is invincible a fair part of the time, drops mines on the ground, forcing your jumping to be near-perfect, gives you a small window to jump over his floating platform before he slams you into the wall (while he's spraying a circle of lasers the entire time), and only gives you equally brief windows where he's guaranteed to not be shielded.
* Agile's first fight is possibly the easiest of the three, but can still be something of a challenge for the unprepared. His slash beams take up a good half of the screen, and the lower of the two possible paths looks as if it will sail over your head if you just stand still, but will still hit you (you have to dash into them to get low enough to avoid them), something that will probably catch a first-time player off-guard.

* Crush Crawfish, mainly because if he grabs the player character with his huge pincers and crush them as his name implies. He can deal a serious amount of damage it's not even funny (you can struggle out if it, though). And if the player character tries to evade from his painful pinching attack, he throws some boomerang-like object to bring the player back down!
* If you defeat Bit and Byte with their weakness, then you'll be able to skip the battle against Godkarmachine O Inary and fight the Press Disposer, if you don't, you're in trouble at the end of Doppler Stage 1. The Godkarmachine O Inary is a formidable opponent on the SNES version who can do major damage to you if you're not quick enough to dodge his attacks, but on the Playstation remake which is also on the Mega Man X collection disk this boss becomes a real ''nightmare''. It's attack, defense, and speed are ''much'' higher than they should be, and even with the [[SuperMode Gold Armor]] found in this respective level, this boss might require multiple sub-tanks to defeat if you're not careful, as its damage output easily rivals the FinalBoss Sigma's.
* Sigma and Kaiser Sigma. Sigma's swapped out his Z-Saber and WolverineClaws for a CaptainAmerica-esque shield, which [[LuckilyMyShieldWillProtectMe defends him from all attacks as long as it's bared]]. His main attack consists of spraying fireballs all over the place, which have an unpredictable pattern and do ''huge'' damage. They can be avoided by air-dashing to the wall Sigma's adjacent to, so of course he begins throwing his shield to knock you out of the sky. And when you do bring him down, you get to face Kaiser Sigma, who takes up a quarter of the screen, fills another quarter of it with floating mines, takes another chunk with shots from his cannons, has a weak spot about the size of a pinhead, and keeps his back to you for half the match. Defeating him is not enough, as you have to do an escape segment with rising inferno eager to nip away your last few bars of health while Sigma's soul threatens to possess X's body to replace its own. He may be the final boss, but he's considered to be easily the worst of all the SNES games.

* Isaz and Sowilo, the tank boss at the end of the second fortress stage; it has two faces that must be destroyed to be defeated, and both requires the usage of both characters to hit. Sounds awesome, right? '''WRONG.''' The tank takes up a ''good'' portion of the screen, and spends ''much'' of the battle restricting your movement space on the very left edge of the screen on top of the moving platform, and can only be pushed back by using Zero's sabre or if enough time passes. The upper face shoots a set of three energy balls that are almost impossible to dodge, while the lower face shoots a missile upwards that then comes down on your position. Between this, and the fact that the projectiles actually ''move with the boss'' when Zero pushes him back, and you have one of the more poorly coded bosses since the Buebeam Trap from ''VideoGame/MegaMan2'' and Doc Robot's Wood Man form from ''VideoGame/MegaMan3''.

* Magma Dragoon considering he has both the fire based [[{{StreetFighter}} Hadoken (Fireball) and Shuryuken (Dragon Punch)]] and loves to constantly use these moves. This isn't even the best part as when he gets hurt enough he'll shoot out a large stream of fire, or summon a fiery meteor storm that is pretty much impossible to dodge. This is take UpToEleven with Zero who has to slash him at close-range, unlike X who can easily fight him from a decent distance away.
** As a nod to just ''how'' tough he is, the game will allow you to enter this battle with ''[[PoweredArmor Ride Armor]]''. Which you ''will'' lose to the aforementioned stream of fire attack unless you enter the lava behind him quickly, and the Ride Armor isn't exactly good in the speed department. Still, you can knock off a good portion of Dragoon's health before you inevitably have to finish the job on foot.
* Zero finds some of his bosses tougher considering that he is suitable for advanced player, especially because he doesn't get their weakness. The aforementioned Magma Dragoon is weak to Storm Owl's weapon... for X, who gets the Double Cyclone. Zero only gets the ability to cancel shots with his saber, which does no extra damage to Dragoon. Same goes for Jet Stingray's weapon against Slash Beast, X gets the Ground Hunter that breaks Slash Beast's claw, Zero gets an Air Dash that does no damage.
* Sigma's an exhausting grudge match, with ''three'' forms, the last consisting of two separate bosses that switch in and out of the fight and do NOT share health, and no breaks in between. The first form goes down easily enough, but the second delights in chasing you around with his SinisterScythe and filling the screen with projectiles, and the third? Each form stays on screen for maybe thirty seconds at a time, and alternates with three robot heads who try to knock off bits of your health and never stay dead for good. One of the two forms is prone to busting out a nasty laser attack with maybe a second's window for dodging, and the second has a nearly unavoidable garbage-spray and an attack that can knock you into some (non-lethal but very painful) spikes. And while X can tear through the first two forms with ease and at least keep the last at a safe distance, Zero has to deal with these things ''up close.''

* The Skiver/Spiral Pegasus, which is basically a tougher version of Storm Eagle, he boasts the same sort of attacks, but all vastly more difficult, coming from all directions at high speeds. And making him a standout from every other boss in the entire series, he does not have an actual weakness to a specific power. Instead, he can be frozen with the Dark Hold, which doesn't last long enough to punch off a decent portion of his health.
** To make up for the fact that he doesn't have similar pushing abilities as Storm Eagle, any contact with him will push X to ''a lot farther''. Did you collide into him next to a pit? You're probably going into that pit.
* Shadow Devil in the first virus stage, it is hard for X, but a NIGHTMARE for Zero. Besides a very hard-to-dodge spam attack, his weak point is his eye, which fires yellow orbs at you, and the most effective attack against him is lightning. X has his buster and Tri-Thunder weapon, both of which are ranged, but Zero has to use his saber and the E-Blade, which he slashes upwards while moving forward slightly. This means he has to get practically in the boss's face to use it, but far enough away not to touch the body (which deals massive damage). Add to the fact that sometimes the eye appears in a place which you plain can't reach with the saber, and you get a very difficult boss for Zero to counter. The [[BoringButPractical C-Sword]] can be used as an alternative, but makes matters no less difficult.
** Shadow Devil also leaves a green outline behind when it splits... that does a LUDICROUS amount of collision damage to you.

* Infinity Mijinion, whose main gimmick is cloning an infinite amount of himself. His clones have the uncanny ability to get in your way a whole bunch until you forget which one's the real one. Even getting to him is a huge problem because the entire stage is spent fighting Illumina, which is no walk in the park either. Heck, this is a case in which using the boss' weakness probably makes the battle ''harder''. Hitting him with the uncharged Guard Shell is difficult, if only because it only works against one of his attacks (which is unpredictable to use, mind you), but if it ''does'' hit, it ''creates another clone''. It wouldn't even be that bad if the clones didn't have so much health, usually taking three charged normal shots to destroy.
** This is taken UpToEleven with Zero if Infinity Mijinion does his ultimate move and hovers in the air in the middle of the room dropping an endless amount of clones. X can at least stay on the wall and shoot him, but Zero has to do a huge wall jump from the top of the wall and strike him in midair.
* [[MostAnnoyingSound DESU BORU!!]] Er... High Max. "Hmm... What's this glowing crystal-like thing here? Oh, wow! Haven't been here before. Guess I can fight the main boss later. Huh? A door? Must be the main boss. Wait a minute... Pfft! This guy's no problem... Oh, wait. I don't have any weapons on me, and I need them. Like, at all. [[UnwinnableByMistake Time to kill myself!]]"
** Basically, High Max isn't that much of a challenge in terms of his attacks, at least not as much as he is annoying. He's impossible to beat without any boss weapons, and even then, he only takes a small amount of damage. Zero has to stun him with a boss attack then slash him, which leads to doing pretty low damage, unless you can stun him when he's low enough to peg him with the Z-Buster (which deals far more damage in one shot at point blank than a single slash from the Z-Saber).
*** When he TurnsRed you're spared the tedious "stun and hit" cycle from before and can hurt him anytime, but he turns into TheBerserker. He floats in the center of the room, spawning four orbs around him at a time and fires them at you one by one in a barrage. If you were too clumsy during the rest of the fight, this attack will kill you very quickly. But when he's fought again in [[ThatOneLevel Gate's Laboratory]] is where controllers start being broken. He gains a barrier that has to be destroyed before the player can deal serious damage, which he can fire to the side and crush the player with. He also gains a watered-down variant of his final attack, which he can use during his "Energy Sphere (DESU BORU (or Death Ball))" attack. Unless you can finish him off in short order, you will die--again, and again, and again. [[spoiler:Although if you know how to do it (short hop with Ensuizan for Zero), the final fight turns into a BreatherBoss, since you can lock him up in what amounts to an infinite that he has no answer to, making the whole affair trivial.]]
* Nightmare Snake, the {{Sub Boss}} of Blaze Heatnix's stage. Which you fight '''5''' times over the course of the entire stage, with exactly 1 segment that doesn't involve fighting it or the actual boss. The worst offender is the part where you fight it while forced-scrolling upwards on very small footholds. Which the sub-boss is bigger than. There is also insta-kill lava ''covering half the fucking screen.'' [[spoiler:However, Rekkoha and a charged Ray Arrow or Metal Anchor will eviscerate their health bar in a matter of seconds.]]
* Gate is quite unpredictable, and has total invulnerability to all of attacks save for [[TennisBoss his energy sphere attack.]] At that, he spends most of the time flying into you rather than using it. His attacks are extremely difficult to predict and retaliate with, since they need to be level with him, and then hit him in the face as they break from damage. [[MalevolentArchitecture Try doing all that over a bottomless pit where the only footing you'll ever get is a handful of small ledges.]] The "gates" that he spawns that you're supposed to damage him with don't make the battle any easier. One follows around the room, another fires at you, yet another pulls you toward it, and they explode in six different directions, meaning you're likely going to be hit in one of them. When he TurnsRed, he gains an attack that destroys those tiny little ledges that you're supposed to land on. Sub-Tanks are more or less a waste, since the usual cause of death here will be falling to your death due to Gate or his attacks flying into you. At least the game grants a tiny bit of mercy by giving you bottomless pit invincibility when you defeat him.
* The Nightmare Mother is already a rather hard boss on Normal mode, it is made even harder in Xtreme mode. Both cubes move at an accelerated speed even at full health and can change direction whenever they like, all while constantly firing projectiles at you until they stop. When they do stop to attack, welcome to BulletHell. Each eye can release one of four attacks:
** Shockwave-producing Blue Orbs: This is the easiest attack to dodge, as the projectiles are slow and predictable. However, it's easy for them to sneak up on you when you are dodging one of the other three attacks.
** Fireball Rain: The eye will unload fireballs into the air, where they will fall upon you like a fountain. The pattern isn't random, but it is unforgivably fast, and you have little room to dodge. This becomes a much worse problem when you have another attack to dodge.
** Flaming Floor: Exactly what it sounds like. The floor is covered in fire, forcing you to take to the walls. Again, this is only to cut off your dodge room for whatever other attack may be coming your way.
** Lightning Orbs: The worst attack. The orbs will hover back and forth halfway from the ceiling and fire lightning at random. This is nasty because there's no timing to them, and it's not telegraphed. The only way to know if the orb is about to fire is if you've already been hit by it.

* Snipe Anteater. On paper, his weakness was the Moving Wheel. In the game, hitting him with weakness is difficult. Even if you could, it actually did little amount of damage than a fully charged X-Buster. However, X not available from start. On top of that, he doesn't have a stun animation, meaning that he can counter your attacks ''as they hit him''.
* Then there is Flame Hyenard. You had to damage a mech traveling over hot lava so you could get to him. This is easier said than done since the camera can screw you over. Then you fight Flame Hyenard. He splits himself into clones that shout [[MostAnnoyingSound "BURN! BURN TO THE GROUND!"]] The weapon he's weak against actually works, but if you're using X or Axl, you'll run out of ammo long before he is dead. And he has a ScrappyLevel to boot!
* And then there is Red. If you don't have Zero, good luck to you. You have to target Red from a distance. Since the camera enjoys screwing you, this becomes a problem. Dodging his attacks is problematic because you're not fighting on solid ground. You're fighting on platforms with a hole in between each one. Fall and you die. Get hit while jumping and you will die. He constantly teleports around on those platforms and there is no way to predict where he will end up. The only way to finish the fight quickly is to use Zero and take contact while slashing him.

!!''Mega Man X8''
* Ravemanta, the manta ray airship in Avalanche Yeti's stage. It takes long time to kill, and appears twice in the stage. The first time it's a fairly tame fight, but in the second encounter it drops bombs that bounce towards you, and has a longer period of time before it becomes vulnerable to attack.
* Bamboo Pandamonium. He's tall enough that you can't get behind him without taking a hit, and has attacks that take up big chunks of the screen. Also, when he take enough damage, he will try to lunge at the player, [[OneHitKO almost instant death if it contacts]] if you don't have any Life Ups. It's more bearable with the Ride Armor... [[GuideDangIt if you knew you could take it with you to the boss.]] And you don't have access to it at all in the BossRush, so good luck with that.
* [[spoiler:Lumine]]. He comes after ThatOneLevel, and is fought directly after Sigma, who's hard enough to begin with. He has two forms; the first one uses the Overdrive of the first 8 bosses except some are modified to last longer; when Burn Rooster's attack comes out, it lasts for the duration of the match. In other words, once it happens the walls are off limits. Additionally, he himself is always moving, making it hard to hit him. Once you've drained his health, he enters the second form, which has a multitude of {{Bullet Hell}}-like laser attacks (one of which lasts a long time and then ''comes back in reverse''), has no notable weakness and is difficult to get a bead on. On his trump card he triggers [[DesperationAttack Paradise Lost]], which will outright [[RocksFallEverybodyDies finish you off]] if you don't do the same to him in 30 seconds. And the player has to know they had to [[spoiler:[[GuideDangIt have Axl finish him with a Doubleteam as a prerequisite for the secret ending]]]]?

[[folder: ''Mega Man Legends'' series]]
* There are two times in the game where you are forced to fight from a slow-moving vehicle and defeat several enemies and then a boss fight, while protecting your vehicle from the attacks. If the vehicle is destroyed, [[NonStandardGameOver it is an automatic Game Over]].
** The first one is from a boat, and you're fighting several submarines and a few Draches, which can shoot torpedoes at your boat. After that, you fight the Balkon Gerät, a giant frog battleship-mecha, which will merrily chop your boat to pieces if you can't dish out damage fast enough. It's tame enough that you can get by with just your buster in Normal if you know what you're doing, but on Hard the entire thing basically mandates a maxed out Machine Buster and Hyper Cartridge to refresh your ammo for it.
** The battle against the Gesellschaft takes this UpToEleven. You have to fight several Draches, the Gesellschaft itself, and then the HumongousMecha Focke-Wulf, one after another, with no continue points or opportunities to heal. You have to do it from the top of the Flutter, which is a small confined space and offers no defensive cover. The Flutter ''itself'' can take damage, there's no way of healing it, if it's shot down it's GameOver, and the ''enemies specifically target the Flutter over you''. You're also ''cut off'' from the town and any resources since the boss fight happens ''as you are leaving the dungeon and returning to town''. It is [[UnwinnableByInsanity technically possible]] to sabotage yourself so badly that you have no chance of winning, but fortunately even without being able to go back to town, they are very possible to take down by developing [[MoreDakka superior firepower]].
** What's especially aggravating about the Focke-Wulf is that if you get hit by one missile, you're pretty much guaranteed to get hit by all the remaining ones as well since they're fired so close together.
* The Karumuna Bash trio, three doglike Reaverbots in the Sub-gate of the Clozer Wood. Those things are ''nasty'' if you're not CrazyPrepared for them. They all attack you at once and they are FAST. Their primary attack is jumping at you, which knocks Mega Man down and is possibly also a CameraScrew if you land right. Their other attack is to ''breathe fire'', which instantly depletes your life meter's shield so you can take MORE damage from their jump attack.

!!''Mega Man Legends 2''
* The train battle. You have to chase down the enemy train, taking on each independent train car as it's own separate boss, all the while protecting your own train from an inane amount of artillery and homing missiles. When you finally reach the engine, even a shot ''from the most powered up weapon in the game'' barely drains a slight sliver from it's health bar. All in all, the fight takes about ''two solid hours'' of holding the fire button and dodging projectiles. And if you die, even at any part, it's back to the beginning of the fight.

!!''The Misadventures of Tron Bonne''


[[folder: ''Mega Man Battle Network'' series]]

!!''Mega Man Battle Network''

!!''VideoGame/MegaManBattleNetwork 2''
* [=QuickMan.EXE=]. The name alone should key you in to how annoying he's going to be. He is invincible at all times except during his attack frames, moves like a spastic monkey on crack, and his attacks are irritating to dodge, because [[{{ShapedLikeItself}} Quick Boomerangs are really, REALLY fast moving]] It doesn't help that he's the second boss of the game, the first boss was a complete chump, and the next boss AFTER him isn't exactly threatening either, so he's not even really a WakeUpCallBoss... Worse yet, it's ''entirely'' possible for the game to be UnwinnableByMistake here, as you can't leave his area (either to recover HP or improve your moveset) once you enter (but nothing stops saving...)

!!''Mega Man Battle Network 3''
* [=DrillMan.EXE=] makes the game a nightmare. He has lower HP than most bosses, but that's because frontal attacks have no effect - his drill is always blocking frontal attacks, so you have to go ''around'' the drill with WideSwords and such. Only a handful of chips can bypass his drill, so good luck having one in advance when he appears!
* [=DrillMan.EXE=]'s ''younger brother'' [=BubbleMan=].EXE is seventeen times as annoying! The bubble spam, the bubble spam! Aaaaaaaaaah!
** To elaborate, he never leaves the back row and the center tile on his side is a hole from which spout an infinite number of bubbles, which block shots and home in on you, always moving into your row so as to block your line of fire at Bubbleman. Since they're limited by number on screen if you stand there shooting them they'll just spawn faster. Meanwhile Bubbleman is using his ''own'' attacks on poor distracted Mega Man. Luckily the electric-element first boss has a megachip that can hit and stun Bubbleman no matter where he hides.
** And that's not even taking into account [=BubbleMan v3=], who almost ascends to GoddamnedBoss status. You can't even ''find'' him unless [[spoiler:you have less than 1/4 of your max HP.]] Frickin' bastard.
* [[http://megaman.wikia.com/wiki/KingMan.EXE KingMan]] is the second hardest boss. He hides in the far back row while his nearly invincible, regenerating chess pieces attack you and block your spaces. If that wasn't annoying enough, if you stay in the back row (the easiest way to avoid his chess pieces), Kingman has a "plan B" attack, where he summons some new chess pieces and ''permanently steals an entire row of your area''. Not even Bass' auras can compare to this guy's cheapness. But it's okay, break type chips can destroy his chess pieces...just kidding, if you figure this out and try it, he'll use a different and more vicious set against you.
* The mandatory [=BeastMan=] Beta battle is friggin' unfair. Beastman moves rather fast around the screen, and will leap into your side of the field to attack (he likes to go behind you). Now, hitting him isn't as hard as it sounds, but he still is fast and deals a lot of damage.
* Flame Man has two candles on his back row, each of which have about 20 HP or so, and revive after a short amount of time. They have different effects depending [[ColorCodedForYourConvenience on their color]], and if even ONE of them is Green, he's invincible. If one's Red, he recovers HP steadily, and if one's yellow, then fire appears in your area and limits your movement range. Even worse, he can have two of the same candle, which means he can be recovering HP AND invincible at the same time. And his attacks are designed to take advantage of this.
* You have to fight Bass twice in the storyline, though the first one is just a HopelessBossFight (you can't hurt him, and even you use something that makes invincible, his attacks ignore it), the second fight however is a pain to get through because he still has his Life Aura, and he attacks ridiculously hard so it may take you a few tries if you don't have the right chip folder and he comes right before you fight [[FinalBoss Alpha]], which if you lose, you'll have to fight Bass AGAIN.
** What makes these two fights especially annoying that Bass has an Aura that can only be removed temporarily using an attack with over 100 power (permanently with a near-impossible to obtain chip), while Alpha has a shield that requires multiple consecutive hits to remove. Hope you brought a deck with both high damage ''and'' rapid firing chips!
*** Though Bass is somewhat easier compared to BubbleMan, DrillMan and KingMan. Breaking chips are not common until 4,and those chips would help a lot against those three. Bass has no such resistance; LifeAura can be chipped away by any strong chip or NorthWind (blows auras away).

!!''Mega Man Battle Network 4''
* Duo's Meteo Fist attack, and by extension Nebula Grey's[[note]]from Battle Network 5[[/note]] dragon attack can easily make the fight unwinnable if you don't have Air Shoes or a Panel Return handy, since your field is cracked to the point where you can't dodge anything.
** That's not the only way the fight against Duo can become unwinnable. Thanks to the game's NewGamePlus structure you'll fight Duo in a "normal" playthrough with more-or-less the chips you'd get in the first third of one of the other games, and when you fight him on a NewGamePlus he'll have his health scaled up to truly ridiculous levels. A MarathonBoss is fine for a final boss normally, but problematic in the Battle Network series because no matter how long the battle lasts you can ONLY draw thirty chips. If you don't pack your folder with thirty of the most damaging chips/combos in your library (and then consistently hit with them, as they likely won't be the easiest to connect with), or throw too much defense in your folder, you will ''run out of attacks'' before he runs out of health. For the third fight you pretty much need a top tier combo folder out of a strategy guide just to deal enough damage, never mind actually ''fighting'' him with it. Oh, and if you're relying on drawing just the right combo in the same hand, for a PA or a powered-up megachip, you'll have to fight another boss right before him every time you get unlucky. Or miss.

!!''Mega Man Battle Network 5''
* [=CloudMan.EXE=] evidently took cues from Bubbleman.EXE. He stays in the back row, protected by clouds that periodically shoot electricity. The clouds don't have much health, but despite this [[TheComputerIsACheatingBastard can take infinite punishment from time-stopping Chips.]] He can also hide in a cloud while summoning a [[AdvancingWallOfDoom pillar of clouds that chases you around]], and the pillar remains even after Cloudman stops hiding.

!!''Mega Man Battle Network 6''

!!''Mega Man Network Transmission''
* [=BrightMan.EXE=], the first boss to put up shields to your attacks. Whereas the previous bosses were dodging and slapping the boss hard enough before they got you, Bright Man will ''murder'' you if you try the tactics that worked on the previous bosses and indeed, some of the other bosses you can fight at the same time. And the bosses get craftier, more agile or with more invincibility shielding from there, making Brightman a WakeUpCallBoss.
* [=StarMan.EXE=] isn't one of the bosses that can shield your attacks, but he compensates that by teleporting around and floating out of range most of the time, not only that, but one of his two attacks involves dropping meteors diagonally on the screen, sometimes being even impossible to dodge and he LOVES to spam them, and every time he uses the attack he also teleports. It gets even worse when he's on low health because he drops A LOT more meteors that fill most of the screen and are almost always undodgeable, and if anything he likes to spam them even more at this point.

[[folder: ''Mega Man Zero'' series]]
* Aztec Falcon, the [[StarterVillain first mission boss]] is seemingly insurmountable the first time you fight him. You have no charge attack (unless you spent time grinding it out by going back to the Underground Lab; if you're playing on Hard, you're screwed), he isn't vulnerable to combos, and the Z-Buster actually ''bounces off'' when the chance to shoot him presents itself, if you're not aiming for the tiny hitbox that is his head. Ah, yes - did we mention he is also a ''TimeLimitBoss''?
* Phantom is spectacularly cheap compared to his fellow Guardians. Three of the Guardians have an elemental weakness which makes beating them fairly simple. Not Phantom. He's neutral, so it takes longer to kill him. Worse, the other Guardians can have most of their attacks interrupted. Only Phantom's dash attack can be interrupted. It is technically possible to interrupt his DopplegangerSpin technique with a charged blow, but for added cheapness Phantom will break the technique and strike you should you close in to attempt it. Speaking of the dash attack, he'll often do it until you hit him, and he charges to your position. If you don't hit him right off the bat, he'll get at least one hit in, maybe more if you don't score a knockback hit. Finally, his DesperationAttack makes him invisible, during which he'll throw kunai at you from random points on the screen. What's worse, he may potentially position himself above the reach of your weapons, or just plain ''above you''. To top this, he has a KaizoTrap ability in the second battle.
** Amusingly, by the time you get to face him again in the third game, there are several upgrades available (ie, Shadow Dash) that render him a pushover.
* Then the Rainbow Devil shows up. It's just as cheap as previous models. It has an especially annoying attack where it bounces around the room, splits into two parts, then into four before finally reforming. It also has a punch attack that crosses nearly half the arena and a projectile attack that makes nearly the entire ground a danger zone. Good times. Thankfully, the redux in ''Zero 2'' is actually somewhat easier.

!!''Mega Man Zero 2''
* Phoenix Magnion is plain ridiculous. He has an arena which periodically spews fireballs from the floor, for starters. You can arrange it so the floor is blocked the first time you fight him, but not the second time. What's worse, he ''dodges every attack'' if he's sitting still. He literally cannot be hit unless he's attacking. And when he dodges, he counterattacks with very wide-area abilities.
** He's an Expy of M. Bison, which helps explain his difficulty (Of course). That huge fireball he "shoots" after dodging backwards is the Psycho Crusher.
* Kuwagust Anchus on Hard Mode is just ''insane''! Not only is he really fast and powerful (two hits = dead, period), but he's the boss of a long and grueling ThatOneLevel. And he has an attack which cannot be avoided, meaning you have to get him to change his flight path. The only way to do this is to either shoot him with the buster enough times, which takes better timing than God to pull off, or deflect him with the Chain Rod. [[GuideDangIt As if you're just supposed to know this out of hand.]] And he'll keep using this attack untill you die.

!!''Mega Man Zero 3''

!!''Mega Man Zero 4''
* Kraft from ''Zero 4'' is a nightmare to fight against. The grenades, the laser rifle that requires you to dash underneath it with split second timing, the giant knife that damages you as it throws you across the arena, the missiles, and the fact that he's one of the few bosses willing to get right directly up in your face on a non-scrolling single-screen battlefield are awful.
** He's also fought in an open area with no walls, so there's no wall jumping away from him.
* Heat Genblem, a fire-based turtle Reploid who has invulnerable periods while spinning with a fiery shell and ricochets off walls to hit you. His most damaging move is a laser that circles the entire screen multiple times, the only way out of this being to display extremely fancy footwork and use the walls to loop up and around him.

[[folder: ''Mega Man ZX'' series]]
* Serpent's two forms on hard mode. This sounds like a given, but you're lucky to survive more than two hits from much of anything in this mode, which also means [[ThatOneLevel just reaching the end of his level is an ordeal]]. His first form was made eye-poppingly fast, and while the second form is only minimally altered, you'll still need almost a perfect run to win.

!!''Mega Man ZX Advent''
* Basically every boss in this game elevates to this level in [[BossRush Boss Survival mode]]. You're given only the default-length life and weapon gauges, two sub tanks, and a single life to try and kill 16 bosses in a row. Damage carries over between fights, so for the most part if you get hit more than once before getting to the Enemy Mega Men - and that's 8 full boss fights to that point - you're probably screwed. With such little room for error, suddenly the game's more abuseable techniques (Time Bomb, ZX spinning slash, ect.) don't seem so broken to spam.
* The Spidrill miniboss! It breaks the floor (which, in addition to removing a quarter of your standing space, can affect whether or not you unlock a vital checkpoint so that you ''never have to do that again''), the walls have got spikes on, it summons miniatures of itself, and it has an irritating tendency to spam a move that spins its legs around. The upgraded Spidrill Neo fight in the Quarry is comparatively easy for nixing the first two aspects and coming right after you unlock [[GameBreaker Model ZX]].
* Chronoforce on Expert starts the fight with Time Bomb, and it never wears off, so he's always in turbo speed. What's more, you know that spreading icicle move he does that you were able to jump between on Normal? Now he shoots two sets of icicles, the second set covering all the angles the first doesn't, making a roughly 90-degree arc that's really tough to avoid whether you try jumping between them or dashing underneath Chronoforce to get past them entirely. And may God help you if you haven't figured out the trick to dodging his attack where he shoots a whole volley of exploding icicles at you from the background, then rewinds them to un-explode and hit you again.
** Even worse? He uses Time Bomb ''again'' right before he uses that attack. The good thing? The ones used at the start of those attacks can actually wear off (only after he's done with the attack, of course) and he only uses it twice, once at slightly beneath half health and the other about two charged shots before death.
* Aeolus. Not for his relatively tame attack pattern, though [[StealthPun lightning reflexes]] might be needed to get out of his slashing attacks (the brief pause between all of his moves can sometimes get you pinned into a corner if you're not careful). No, the issue is his ultimate attack that he loves to use and abuse: he floats up in the corner of the screen and traps you between two lightning pinwheels that spin in the same direction. Once he starts this you can't stop it, and from the ground you have little choice but to try and dash between the uneven lightning rotation (good luck). You can certainly trivialize the attack itself if you turn into Queenbee and fly up fast enough (assuming you haven't already burnt up the weapon gauge), but then you still can't even ''hit'' Aeolus until he drops to the ground. By extension, this makes [[GameBreaker Time Bomb]] unhelpful. All in all, he's a surprisingly GenreSavvy bastard.


[[folder: ''Mega Man Star Force'' series]]
* A battle with [[DualBoss three]] level 3 Jammers happens during the endgame. They have above-average HP and fast attacks. While not too complex, they can overwhelm and quickly end you with their punches and machine guns if you make mistakes. If you die you may even lose some progress because the battle happens [[DifficultySpike out of nowhere]] during a long period without Geo asking to save the game.

!!''Mega Man Star Force 3''
* Acid Ace. He has a huge repertoire of moves, with something to break ''any'' Noise, and he doesn't follow a clear pattern with them. Then there's the matter of his R form, which is fought directly after Dread Joker R without a chance for you to heal.
* Similar to the Jammer fight above, there is a fight with two Noise Wizards, one level 3 and one level 4[[note]]they go up to 6, but 4 is the strongest until the postgame[[/note]]. The level 4 one has an attack that cracks panels, so you can easily run out of room to dodge and just get barraged constantly by their sword and gun attacks, which they can combo between and just constantly put the pressure on you. It can be shocking how difficult this fight is, because Noise Wizards aren't usually a threat when fought one-on-one.
* Apollo Flame. (He's also in the second game, but he's the final BonusBoss there as opposed to being fought halfway through the postgame.) He has a lot of HP, a barrier that regenerates, and a lot of attacks that either can't be blocked or keep you from hitting him until his barrier comes back. It's easier if you have Cancer or Virgo Noise, and infinitely harder if you have Ophiuca or Wolf Noise.

[[folder:Fan Games]]
* Jet Man. He spents most of the fight out of your reach, and he has lightning-fast missiles and a whole cargo load of bombs in his arsenal that require precision and perfect timing to avoid. Good luck doing a NoDamageRun against this guy!
* Glue Man fights a lot like Concrete Man from ''Mega Man 9''. He fires Glue Shots at you to freeze you while at the same time sliding all around the arena trying to ram you for MASSIVE CollisionDamage.
* Comet Woman isn't too bad in her first fight, but she becomes exponentially harder in the BossRush. Without the low gravity from her stage, she's able to move much faster, her orbiting shield attack becomes harder to avoid, and you'll spend more of the fight with those orbiting balls around you blocking your shots.
* The GiantEnemyCrab from Occupied Wily Stage 1. It pays homage to the Mecha Dragon from ''Mega Man 2'', but ramps the difficulty UpToEleven. You have to use the three ladders to avoid the energy balls the crab shoots out, but it also has another attack where it electrifies one of the ladders. If you get hit by anything while you're on the ladders, the knockback will push you right into the pit, and there's no safety platform like the Mecha Dragon fight.
* The squid boss from Occupied Wily Stage 2 has a OneHitKill move where it rams its head (which you have to stand on in order to fight it) into the ceiling, and it requires a precise jump off to the side of the boss gate in order to avoid it. The later you jump, the more likely you will be to hit the ceiling and fall into the pit, but if you jump too early, the squid will be too high to catch you. Even then, you're still fighting it on a small platform with bubbles from its mouth and plasma balls from its tentacles, making it very easy to get hit and even then you could still get knocked into a pit.
* The Wily Machine is probably the hardest version of Wily since his capsule from ''Mega Man 7''. The first phase has a weak spot that is out of reach of the Mega Buster, so you need an upward-reaching weapon to hit him, and he takes up about ''three fourths of the screen'', giving you little room to dodge his attacks.
** The second phase is even worse. The Wily Walker's weak spot is only visible for a couple seconds when it jumps, and it's random where it's going to jump next. Each time after it jumps it will charge at you. If it jumps all the way to the other side of the arena, it will dash at you, and you can slow it down with the Mega Buster in that case, but if it lands somewhere in the middle it will just walk at you which can't be slowed down. If you're not behind it when it does this, you need a perfectly-timed Comet Dash or Rush Coil to avoid it.
* The first phase of [[spoiler:the Remir Machine]]. The only way to damage it is to turn on the spikes in the room and get it to step on them, while at the same time avoiding its two massive hitboxes and the bullets it fires from the top of the screen, and also making sure ''you'' don't fall into the spikes.