Unwinnable by Mistake/Video Games/Mega Man

Mega Man

 * The very first Mega Man 1 game has one of these: in Elec Man's stage, there is an item called the Magnet Beam hidden behind some blocks, which require you to have beaten Guts Man before you can remove them. A level near the end of the game is impossible to complete without this item, and there's no way to go back and get it. Even better, you have to have one of two specific weapons to get the item; if you go through the stages in the wrong order, then you have to visit this stage (and fight its boss) twice.
 * That is, unless you're able to take advantage of a game-breaking glitch which allows you to zip through walls and other boundaries.
 * Amusingly enough, once you gain the Magnet Beam, such zipping becomes easier to do, even allowing you to skip all the boss rematches.
 * You can still go back for the Magnet Beam by losing all your lives and choosing a new stage from the Game Over screen. You can also avoid fighting Elec Man again with another Game Over after collecting the Magnet Beam. You do lose your score this way, however; and first-time players may have forgotten all about that suspicious object trapped inside the wall by the time they reach Dr. Wily's castle, making this a Guide Dang It.
 * In 2, if you reach the final boss without having enough  energy (from using it all up against earlier enemies in Wily's fortress), fail to connect said weapon with the boss too many times, or were foolish enough to use any other weapon (which restores the boss' health!), then it is impossible to win the last fight. That's not all: when you start your next life, the checkpoint where the game dumps you at has no enemies; therefore, it is impossible to recharge the weapon required to win the fight. Result? Welcome to the game's Hopeless Boss Fight, where you'll have to suicide yourself for the number of lives needed for Game Over. If you reset the game in rage, then you did write down that password to get back into Wily's fortress, right? Oh, and it only puts you back at the beginning of the fortress. To negate this problem, the player can go for the Game Over and then continue; you get all your weapon energy back and start at the beginning of that level instead of the whole fortress.
 * Of course, if you're using "Invincibility" via Game Genie, then you cannot die and thus have to restart. At least it is noted in the code booklet.
 * You could wind up with an unbeatable situation earlier than that. If you reach the fourth Wily stage boss (before Wily himself, of course) without a full complement of Crash Bombs, you are screwed. Not only is it the only weapon that can kill the boss, but it's also the only weapon that can bust through the walls keeping you from shooting the boss in the first place. While the corridor you restart at if you lose a life to it is full of enemies for you to restock your energy on, they're some of most annoying and powerful enemies in the game; any attempt to restock your Crash Bomb energy with them is a battle of attrition.
 * You have just enough Crash Bombs to break the walls and kill the boss turrets, and no more -- and there are more walls than you need to break. You also need to climb around the room with the floating platform Items 1 and 3 (jetboard Item 2 in a pinch) while the turrets are shooting at you. You should have more than enough item energy and possibly a few Energy Tanks, but falling down too many times will leave you with no platforms to stand on. And if you miss a single Crash Bomb shot (thankfully, they have a splash radius), then you might as well kill yourself right away to save some weapon energy.
 * The turrets respawn, but the walls do not. Destroying the walls only, either immediately or after missing a shot, is a viable strategy that makes the next life easier.
 * In 3, while revisiting Gemini Man's stage, if you were to drain all weapon energy for Rush Coil and Rush Jet early on, you would come to a wall that's impossible to scale immediately after the first Doc Robot battle. Unless you can cheat using the second controller to clear it, you'd be forced to reset the game.

Mega Man the RPG
The fan-made RPG Maker game, Mega Man: The RPG, has a couple of cases of this, clearly unintended:


 * If you use one of the teleportation items while you're in the raft, then the raft comes with you, which gets it stuck in the square where you land. If you had any need to use the raft to get anywhere, then let's hope you saved before you did that.
 * When you first meet Dr. Wily, it's as Mega Man alone, and it's a Hopeless Boss Fight. Immediately after that, cut to Cut Man and Elec Man finding a way into the same room. Dr. Wily sees them and taunts you; your characters get healed; and the battle begins again, winnable this time. Well, that's what happens if both Cut Man and Elec Man are alive when you get there. If not, then you get a Game Over screen after the taunt, even though the author has stated that they never intended this. To make matters worse, due to another error, the item that's supposed to be a revival item doesn't work as a revival item. Another item, which is meant for healing status ailments, ends up doing that job. Since status ailments are relatively rare and non-threatening in this game, if you didn't know this, then you might not have any of that item.

Mega Man Star Force

 * In the first Mega Man Star Force game, it was possible to get stuck between an NPC and a wall. If you did this while not on a Wave Road, then the only way to get out was to reset and load from your last save; hopefully, you knew better than to save while stuck. Later games fixed this problem by briefly allowing you to run through NPCs if you get stuck.

Mega Man X

 * In Mega Man X 6, the Amazon Area has a portal to an alternate exit. This area requires the air dash ability to cross a bottomless pit. If you reach this area with X's Shadow Armor, which is incapable of air dashing, then you're screwed.
 * The same can be said for Ground Scaravich's Stage. The gimmick of the stage is having a random room every teleport you have to go through. Sometimes, one of the rooms contains a jump that requires Air-dash. If you are wearing the Shadow Armor, or if you're crazy enough, no Armor, you really don't have much choice but to die, and hope the stage doesn't teleport you to that room.
 * The same room can also spit out a gap that requires the Mach Dash ability from the Blade Armor to cross. What's that? You don't have it yet because the fourth part is later on in this level? Too bad!
 * Unless you also happen to have a specific combination of upgrades equipped (Hyper Dash and Speedster) and a specific one NOT equipped (Jumper), meaning you can get through if you know about this beforehand. Oh, and the necessary parts can be Lost Forever if you fail to save the reploid holding them.
 * There's a jump almost exactly like this in the final stages. The same situation can arise, requiring either an air-dash or the parts listed above. The penalty for being unable to perform this jump is much more severe: you'll have to replay quite a few stages and bosses.
 * A similar problem arises if you're trying to get the Dr. Light capsule in Metal Sharkplayer's stage. There is a large chasm you have to jump that requires a certain combination of upgrades, and possibly Blizzard Wolffang's weapon. If you don't have those, then you can't make the jump. Die, and you respawn directly in front of that chasm with no way to get back to the stage's main path. And if you kill your remaining lives off to get a game over, don't hit continue, or else you'll once again respawn in front of the chasm with a full allotment of lives.
 * And for a 6th example, just from X6: It is possible to get locked into a path where you must fight High-Max without having any special weapons available. High-Max is invulnerable if you don't have at least one to use. Your only option, as in the above cases, is to get a game over and return to the stage select screen. Did we mention X6 is generally considered to be a Franchise Killer?