History ThatOneBoss / MegaMan

* Fefnir's EX Skill requires immaculate timing and precision and constant movement to keep jumping where flame columns aren't going to erupt. You literally ''cannot'' afford to take your eyes off the screen at any moment or you may lose track of where to jump! Even the official MMZ2 strategy guide outright calls this move ''"the most nightmarish move in the entire game"''.

* Fefnir's EX Skill requires immaculate timing and precision and constant movement to keep jumping where flame columns aren't going to erupt. You literally ''cannot'' afford to take your eyes off the screen at any moment or you may lose track of where to jump!

* The Yellow Devil from Wily Stage 1. Its 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 — or have to have memorized his pattern — 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, even with powerful weapons like the Thunder Beam, since you will probably get in only one shot.[[note]]Thankfully, the [[GoodBadBugs pause trick exists]] to alleviate this. Just repeatedly pausing and unpausing in this game will allow the MercyInvincibility to be bypassed and allow whatever weapon you use to land an extra hit every time you pause and unpause and the bullet is still in the enemie's hitbox.[[/note]] And when he changes sides after that, you have much less reaction time to dodge with because he's already on screen instead of off of it. And there are two LATER bosses before the final one, and with proper tactics, they aren't nearly as bad as this one.

* The Yellow Devil from Wily Stage 1. Its 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 — or have to have memorized his pattern — 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, even with powerful weapons like the Thunder Beam, since you will probably get in only one shot. And when he changes sides after that, you have much less reaction time to dodge with because he's already on screen instead of off of it. And there are two LATER bosses before the final one, and with proper tactics, they aren't nearly as bad as this one.

* Wood Man is also particularly sour. He only has two attacks, but they combo into each other heavily. Wood Man's Leaf Shield is the mother of all HitboxDissonance, and is nearly impossible to jump over without a perfect running start. If you consider cheesing it with Item 1, the falling leaves put a hasty stop to that idea. The shield also blocks projectiles before Wood Man throws it (If only your own Leaf Shield could do that...), so it's hard to use his weakness of Atomic Fire while accounting for this. He's also weak to Air Shooter, but you're very unlikely to have it on hand at the point you first fight him as [[ScissorsCutsRock Air Man's only weakness is Leaf Shield.]]

* Bit is the first of the Nightmare Police encountered and usually the toughest for newcomers, due to him attacking X randomly on one of the earlier stages. At this point, players are most likely ill-equipped to fight him and lacking in terms of power-ups and while Bit's lunge attack is easy to avoid, he can also use projectiles that either lock him in place or auto-aim towards him (and he even send two of said projectiles at the same time). Bit is even more difficult if you aim to finish him using his weakness which is Frost Shield: the projectiles of said weapon are very slow and can most likely hit Bit when he's lunging towards X and can only hit him diagonally due to Bit putting up a shield that protects him from a direct attack

* While the first phase of Wily Machine 4 is very easy and straightforward, the same can't be said about the second phase. Its weak spot (a small gem) can only be reliably hit with a Charged Shot or a Drill Bomb. The latter is its weakness and isn't 100% accurate, as there's a chance the Drill Bomb can hit a little too low and end up just getting deflected, which makes detonating them manually a better option, but [[GuideDangIt neither the game nor the manual mention this is possible]]. There's a way to just sit below the machine without getting damaged whatsoever, but you can't hit it at all without going to its range zone. [[ArsonMurderAndJayWalking And if you're unfortunate enough to use Rain Flush after defeating him and accidentally "kill" Wily]], [[GameBreakingBug the game messes up and you're forced to reset (or you could rewind if you're playing Legacy Collection)]]

* Wily Capsule 7, the FinalBoss, is infamously difficult even by the standards of final bosses for the ''Mega Man'' series. His main attack is shooting four [[ElementalPowers elementally charged]] orbs that [[{{Roboteching}} stop mid-flight to adjust their path twice]], making them extremely difficult to avoid without great amounts of precision. While the electric sphere isn't a huge issue as it does minor damage and has no additional status effects, the ice sphere [[HarmlessFreezing freezes Mega Man in place]], leaving him open to quick and powerful ground-traveling sparks for additional damage, and the fire sphere [[ManOnFire immobiizes Mega Man and sets him ablaze]] as he takes a random amount of continuous damage. His weakness, the Wild Coil, is (as per the tradition) not only difficult to hit him with, but [[CountingBullets if even one shot is missed, it won't have enough energy to defeat him]]. [[WordOfGod Keiji Inafune, the franchise's producer, has admiited to purposefully making this fight insanely hard]], and even playtesters found this one impossible without using at least one E-Tank.

* Magma Dragoon, the boss of the Volcano stage, has a very aggressive moveset that primarily serves as a ShoutOut to ''Franchise/StreetFighter'', with his main two attacks being high and low Hadoukens and a long-range Shoryuken. Whenever he's not doing either of those, he has a fast downward kick, a deadly fire blast across the entire arena, a magma ball he can throw into the magma around the arena to create a temporary OneHitKill pillar, and [[DesperationAttack when his health gets down to half, he can bring down an unpredictable fiery meteor shower]]. While X can easily [[AIBreaker get him stuck in a helpless loop]] with the Double Cyclone, Zero will have to get dangerously close to attack, and the Saber technique he's weak to, the Raijingeki, is both slow to start and makes Zero a sitting duck. The one mercy that Zero can get is that he can bring the Ride Armor into the fight, but it's slow and only has so much health before it's destroyed. It's also not available at all in the rematch with him during tbe final stage's BossRush.

* Thunder Slimer, who is a ''miniboss''. He can glue you to the floor with four blobs of slime sent in all directions, and while you can destroy them with a charged shot or dash out of them, it likely won't be in time to stop him from striking you with lightning, or worse, charging directly at you wherever you are. If you get by him, it will likely be with less than half your health, meaning you'll most likely die at least once before getting to the boss, Spark Mandrill, by which point you'll likely only have one life left and have almost no room to get used to his fighting patterns even if you have his weakness.

* While the first phase of Wily Machine 4 is very easy and straightforward, the same can't be said about the second phase. Its weak spot (a small gem) can only be reliably hit with a Charged Shot or a Drill Bomb. The latter is its weakness and isn't 100% accurate, as there's a chance the Drill Bomb can hit a little too low and end up just getting deflected. There's a way to just sit below the machine without getting damaged whatsoever, but you can't hit it at all without going to its range zone. [[ArsonMurderAndJayWalking And if you're unfortunate enough to use Rain Flush after defeating him and accidentally "kill" Wily]], [[GameBreakingBug the game messes up and you're forced to reset (or you could rewind if you're playing Legacy Collection)]]

* The Nightmare Mother, the boss of the first stage of Gate's Lab. The boss consists of two large invincible cubes with small eyeballs inside of them that rapidly shift around the room either clockwise or counter-clockwise for a while until they stop at a random place. When they do stop to attack by bringing the eyeballs outside of the cubes (the only time they can be hurt), welcome to BulletHell. Each eye can release one of four attacks: shockwave-producing blue orbs, fireball rain, setting the entire floor on fire, and countless amounts of lightning. All of these are ''extremely'' difficult to dodge, and they ''hurt''[[note]]it's a common tactic to just tank the CollisionDamage from the eyeballs themselves while attacking, as they do the least damage out of ''anything'' in the fight[[/note]], and after they're done with the assault, they retreat back into the cubes and start the pattern again, making this fight more of a battle of endurance than anything. When it reaches half health, the cubes move at double speed, making matters even worse.

* While Sigma himself is very pattern-based and easy to read, the true terror appears in the form of Kaiser Sigma, his gigantic battle body. Kaiser Sigma is so large that he fills up half of the arena you fight him in, and his weak spot is [[HitboxDissonance not his head, but rather the small "fins" directly above it]]. He has two patterns, one when you're behind him and one when you're in front of him. When you're behind him, he shoots [[MacrossMissileMassacre many homing missiles that hit extremely hard]], and when you're in front of him, he charges and fires a cone-shaped laser either upward or downward that [[CycleOfHurting continuously damages and stuns you when you get hit by it]]. All the while he's spawning tracking bombs. Only two things can damage him: charged X-Buster shots (in a game where the X-Buster upgrade actually [[PowerUpLetDown makes it more difficult to use]]), and the GameBreaker Z-Saber[[note]]However, acquiring it locks you out of the good ending[[/note]] which can take him down in only two hits, but get hit ''once'' while trying to slash him, and it'll be cancelled out. Even after you manage to kill him, it's not over, as you still have one last trial: wall-climbing a long vertical AutoscrollingLevel with the Sigma Virus trying to knock you into the damaging lava below. If he successfully manages to, it's entirely possible for you to get stuck in hitstun under one of several outcroppings in the shaft, and since the lava is treated as a solid floor, you can get crushed, in which case [[ContinuingIsPainful it's back to the beginning of Sigma's first form]].

* The boss of the first Zero Space stage is the Shadow Devil, a traditional Devil boss from the Classic series turned up to eleven. First, The Shadow Devil has ''six'' different random patterns it can go across the screen with instead of the usual one, and whenever it does, it leaves behind a green outline that if touched, if it doesn't OneHitKill you, it will leave you seriously hurting, greatly restricting your movement range. Secondly, the Shadow Devil can also randomly take the form of Wily Machine 6 at half health, trying to crush you as it moves across the screen. Thirdly, its weakness is Tri-Thunder as X and E-Blade as Zero[[note]]a direct ShoutOut to the very first Yellow Devil's weakness to the Thunder Beam[[/note]], but while X can shoot from a distance, Zero has to attack up close, making it very risky, and sometimes its eye can appear very high or low, only making damaging it even harder. Capcom must've known this, because a ''much'' better strategy as Zero is to use C-Flasher: It's ranged, fast enough to hit twice a cycle, can parry his projectiles, turns any damage you take into more weapon energy, and is ''as strong as his actual weakness.''

* The boss of the first Zero Space stage is the Shadow Devil, a traditional Devil boss from the Classic series turned up to eleven. First, The Shadow Devil has ''six'' different random patterns it can go across the screen with instead of the usual one, and whenever it does, it leaves behind a green outline that if touched, if it doesn't OneHitKill you, it will leave you seriously hurting, greatly restricting your movement range. Secondly, the Shadow Devil can also randomly take the form of Wily Machine 6 at half health, trying to crush you as it moves across the screen. Thirdly, its weakness is Tri-Thunder as X and E-Blade as Zero[[note]]a direct ShoutOut to the very first Yellow Devil's weakness to the Thunder Beam[[/note]], but while X can shoot from a distance, Zero has to attack up close, making it very risky, and sometimes its eye can appear very high or low, only making damaging it even harder. A ''much'' less risky and more efficient strategy as Zero is to use C-Flasher, which does considerable damage and will be refilled by any damage you sustain.

* The boss of the first Zero Space stage is the Shadow Devil, a traditional Devil boss from the Classic series turned up to eleven. First, The Shadow Devil has ''six'' different random patterns it can go across the screen with instead of the usual one, and whenever it does, it leaves behind a green outline that if touched, if it doesn't OneHitKill you, it will leave you seriously hurting, greatly restricting your movement range. Secondly, the Shadow Devil can also randomly take the form of Wily Machine 6 at half health, trying to crush you as it moves across the screen. Thirdly, its weakness is Tri-Thunder as X and E-Blade as Zero[[note]]a direct ShoutOut to the very first Yellow Devil's weakness to the Thunder Beam[[/note]], but while X can shoot from a distance, Zero has to attack up close, making it very risky, and sometimes its eye can appear very high or low, only making damaging it even harder. A ''much'' less risky and more effective strategy as Zero is to use C-Flasher, which does considerable damage and will be refilled by any damage you sustaining.

* The boss of the first Zero Space stage is the Shadow Devil, a traditional Devil boss from the Classic series turned up to eleven. First, The Shadow Devil has ''six'' different random patterns it can go across the screen with instead of the usual one, and whenever it does, it leaves behind a green outline that if touched, if it doesn't OneHitKill you, it will leave you seriously hurting, greatly restricting your movement range. Secondly, the Shadow Devil can also randomly take the form of Wily Machine 6 at half health, trying to crush you as it moves across the screen. Thirdly, its weakness is Tri-Thunder as X and E-Blade as Zero[[note]]a direct ShoutOut to the very first Yellow Devil's weakness to the Thunder Beam[[/note]], but while X can shoot from a distance, Zero has to attack up close, making it very risky, and sometimes its eye can appear very high or low, only making damaging it even harder.