We've reached the point where all normal bosses are available to fight, most of which are returning from Mega Man and Mega Man 2. Let's see how they translated to the Game Boy.
Cut Man is no longer stunned by Mega Man's attacks, nor does he (or anyone else) take extra damage from the Buster. The smaller room makes it tough to find a position that feels safe, but this version of the fight is a little more predictable.
Cut Man now sits still after throwing the Rolling Cutter, and the flat room makes it easier to avoid his jumps. He can be baited into jumping by shooting at him, but he'll jump now and then on his own as well. His downtime while using the cutter makes this a reasonable damage race, but he's not the pushover he used to be.
Fire Storm deals two damage, and while that doesn't sound impressive, staying near him can rack up a lot of hits with the shield. This fight is just about average as this game goes, and it's definitely tougher than the standard Nintendo Entertainment System fight, if only because the reduced floor space makes the player move over or under the boss more often.
This is a great deal easier than his original pattern. Four shots are fired per attack, but only at the highest and lowest points of his movement, creating a wider gap between them. They still deal enough damage to kill in three hits, but he's weak to two weapons (Elec Man's Thunder Beam and Cut Man's Rolling Cutter), and is so simple to dodge that the awkward ice physics aren't even a problem.
While his shots only deal three damage, they're just as hard to avoid as before and Elec Man will happily throw them at you constantly. Oddly, he prefers to jump anytime Mega Man is shooting, and will even cancel his own attack to do so. Mashing the fire button and running from him makes it possible to wear him down without having to worry about the Thunder Beam. As before, Rolling Cutter ruins him.
This is... sad. Fire Man was absurdly powerful in the first game, throwing fire seemingly at random when at range, and retaliating harshly if chased and shot at. This one shoots slowly and consistently, the projectiles leave no flames behind, and running towards him causes him to retreat until he's at the specific range he needs to be.
The only thing stopping a player from running after him and shooting him in the back for the whole fight is that he won't turn around at the same spot each time he reaches the wall, so it's easier to just let him attack than try to time jumps over him. Fire Man certainly needed to be toned down, but this went a little too far. He's weak to the Ice Slasher and Rolling Cutter.
Having reached the teleporter room of Dr. Wily's stage, we find that instead of fighting the starting bosses again, we have a new set from Mega Man 2 to deal with, each giving us their weapon upon defeat.
This was the hardest fight to get good screenshots of, as Bubble Man himself is flickering constantly, and usually has multiple shots on the screen. He fires a bit less frequently, with a maximum of two bubbles, and has no spikes on the ceiling, but is otherwise very close to the original.
This set of bosses is even more challenging with the smaller arena, and Bubble Man will constantly be in the player's way. The last image shows Mega Man taking damage from a normal bullet, penned in by Bubble and a bubble. Quick Boomerangs deal two damage, which is enough to make this easy on a full life bar, but still tough if we've been beat up by the others first.
There really isn't enough room for this attack to be fair anymore. It's barely possible to stand between the flames, and they can be thrown high enough to be almost unavoidable. Heat Man's dash can be dealt with the same way as before, but his projectiles can't be interrupted, and he'll occasionally move just as they land instead of giving us a moment to flee. He's weak to Bubbles, but will take two damage from Quick Boomerangs as well.
Flash Man has roughly the same behaviors as before: Walking back and forth, freezing Mega Man, and running toward Mega Man after every attack and jump. The flat room makes this much easier to deal with though, as he has no ledges to jump over and will run predictably if left alone. He takes two damage from the Ice Slasher, making him the only boss in this set who's weak to something from the first group.
This, along with Bubble Man, is where the smaller room really comes into play. Quick Man always jumps twice, then runs toward Mega Man and stays against the wall for a bit, allowing enough time to damage race him if the player can avoid some of the contact damage through skilled dodging, or deliberately taking hits from the boomerangs. Figuring this out in the middle of such a chaotic fight is another matter.
Attempting to gain distance will quickly lead to getting jumped on and surrounded by projectiles, and early attempts to dodge under him in the middle of the room are going to lead to a lot of contact damage when he runs. Luckily, this game gave him two strong weaknesses. Flash Man's Time Stopper will bring him to half health, and one fully-charged shot from Atomic Fire can finish him off. Fire Man's fire is also useful, as it can get multiple hits in without the player needing to aim.
One more teleporter appears after the rest are defeated, leading to a new boss.
Enker cannot be damaged by special weapons, as he has a gimmick reliant on the Buster. By raising his spear, Enker powers up with the damage he takes, retaliating with a projectile that will be larger depending on how many times he was hit. He will then run across the room, jump across the room, or run/jump halfway, then run/jump again.
This is an unintuitive fight, as the absorption move looks like something to avoid, but is actually the moment where players should be dealing damage. The largest projectile (shown here) is about as hard to dodge as a shot from Fire Man, and Enker's movements are the real threat. He cannot be harmed when running, and is extremely difficult to react to when he moves to the center of the room.
This is an easy fight when treated as a damage race, but leads to a quick death by contact damage if players try not to shoot at his spear.
Overall, these didn't work out that well. Players unfamiliar with the NES games will have a rough time with at least half of them, but the reasons they're hard have more to do with the smaller rooms and higher risk of contact damage. Quick Man can stomp all over the room and easily traps Mega Man in corners, while Bubble Man and Heat Man are much more difficult to avoid without a lot of practice. The universally flat floors made Cut Man and Flash Man less interesting, while Fire Man and Ice Man received needed but overly strong downgrades.
That leaves Elec Man as the only one I feel was improved over his original version. He deals less damage and cannot shoot in air, but remains aggressive. Being able to distract him from using his attack by shooting constantly feels unique, like Toad Man done better, and his jumps are still dangerous.
Enker is a little bit too fast, causing players to guess his next move in a way similar to Shadow Man. Damaging him by shooting him when he seems to want you to is confusing, and this isn't the kind of fight that should come after a tough gauntlet. It's the sort of boss that punishes attempts to approach it carefully, and is better suited to an area than is easier to run through again after a loss.