Each of the revisited stages contains two fights with Doc Robot K-176, who takes on the attack pattern of one of the Robot Masters from Mega Man 2. These aren't quite the same, as Doc's sprite is bigger than even Wood Man, and he's often slightly more difficult in other ways. However, we've got a new set of tools for dealing with him, and each form takes four or more damage from at least two weapons, and he often takes two damage from many others. I'll list the main weaknesses after the names. Metal Man (Magnet Missile, Hard Knuckle)
Doc doesn't get the conveyor belt here, but his Metal Blades are a little faster. The Magnet Missile seems like the obvious choice here, but the Hard Knuckle is surprisingly helpful as well. When fired from the ground, it takes so long to reach the other side of the room that Doc will land again before it gets there. The fight's as fun as it always was, and the weaknesses are well chosen to let the player take advantage of their behavior.
Quick Man (Gemini Laser, Search Snake)
This fight is ridiculous with the Mega Buster, as Mega Man only deals one damage, you're dodging a larger enemy, and if anything Doc is even more energetic than the original. However, the weaknesses are working in your favor again, and they offer two very different ways to approach the fight. Doc spends a lot of time trying to jump on you, making him easy to hit with Search Snake at close range, and using these aggressively will take him down fast. Gemini offers a safer strategy, as you can fire them anywhere with a good chance to hit, leaving the player free to focus on avoiding him. The slide is also a welcome addition for this fight.
Air Man (Magnet Missile, Spark Shock)
Doc seems to be missing one of Air Man's easier attack patterns. Of those that remain, two can be dodged with a jump, the fourth is made much easier with the slide, and the second is now nearly (if not entirely) impossible to dodge from the ground due to the slightly larger hitboxes on the tornadoes. If you're really concerned about taking damage here, Rush Jet allows Mega Man to dodge them near the top of the screen instead.
Doc takes two damage from the Buster so the old tactic of charging in blindly is still viable, though if you're going to do that you might as well use Spark Shock. Magnet Missile allows a more cautious approach, as it can be fired through any gap in the tornadoes for a hit. There's really nothing that can be done to make Spark Shock more interesting, but this is as good a place as any to use it, and we get another great use for Magnet Missile.
Crash Man (Hard Knuckle, Top Spin)
Doc's version is a little more erratic, jumping more often without any action from the player. His aim is a little better too, as he likes to fire a little above Mega Man which is perfect for catching a moving player.
The old strategy still works though, since the slide can deal with his new aiming behavior just fine. This one also takes two damage from the Buster, which is a great change given how boring the safe tactic is. Top Spin can be used here if you want to take the lazy route (and deal with the possibility of losing it all instantly), but there's not much point in it as Hard Knuckle kills him in four hits. They have to be placed well, but it's pretty easy to catch him in the middle of a jump arc since they stay still for a moment.
This fight stands out in quality for being harder is just the right way to complement the new gameplay while also being less tedious with the Buster, and allowing a weakness tactic similar to his original fight that takes a little more skill to pull off.
Flash Man (Needle Cannon, Gemini Laser)
This one is tough. Doc won't jump when shot anymore (though he won't turn around either), so you can't slow him down, and he only takes one damage from the Buster, while his fat sprite is quite a challenge to dodge. Your best bet is to stay on the top platform and jump from the edge when he comes by. The height advantage also makes it easier to avoid his shots. Rush Jet is extremely helpful if you want to play it safe, and it'll last for the whole fight if you keep jumping. Gemini Laser is fun to play with since weapons aren't stopped by the Time Stopper, but Needle Cannon is the better option here since it does the same damage and you'll want to kill him fast. This one's a little too difficult and the weapons don't add anything to the fight, though anything that gives players a good reason to use Rush in a boss fight is nice.
Bubble Man (Spark Shock, Shadow Blade)
Getting through Doc's normal shots is a little more difficult here, but the fight is otherwise unchanged and the slide makes it easier to keep your distance. The Shadow Blade is the perfect weapon for this given how much time he spends hanging above you.
There's an interesting exploit here involving the Rush Marine (or Jet). After landing, Doc won't start firing bubbles again until Mega Man touches the ground, allowing you to hang in front of him and fire away without retaliation. Bubble Man did this in Mega Man 2 as well, though there wasn't a way to use it to your advantage. I don't know if the designers were aware of this, but I could see them deliberately leaving it in just to give Rush Marine a chance to shine.
It's worth mentioning that these last two were great choices for Gemini Man's stage, as the flashing tiles are reminiscent of those in the last game, and it's the only one with water.
Wood Man (Needle Cannon, Hard Knuckle, Search Snake)
The Leaf Shield's leaves are much bigger now, leaving only a pixel or two of space for jumping over them. There's no time to get under him either, making Rush a godsend here. It's also the one time Rush Coil could conceivably be helpful in a fight, though Jet is still the better option. There's not much reason to pick one weapon over another, just get through the leaves and start hitting him with one.
I'd say this is the worst of the rematches, as avoiding the Leaf Shield from the ground is unreasonably difficult, and getting under him without damage is practically out of the question (though just barely possible). Then again, it's nice to see at least one reason to use Rush Coil in combat, as the player might want to save Jet energy for the second half of the stage.
Heat Man (Top Spin, Shadow Blade)
Dodging the initial volley of Atomic Fire is another near-impossible feat, though after that he can be dealt with in the usual pattern by sliding away when he fires. Top Spin kills him in four hits, with Shadow Blades as a safer option if you're low on health. Otherwise, it's the same fight as before. Even his size doesn't come into play here, since he does the same fire transformation to move across the screen.
Though some of these are quite difficult in comparison to what's been expected of us so far, nearly everything can be dealt with using our new set of items. It's really nice to see Rush get some use in combat, and all of the weaknesses allow the player to make the most of the weapon behaviors. Aside from all that, it's just a lot of fun to see new and harder versions of the bosses from the last game and find new ways to fight them, and giving the player a choice between weaknesses is something I wish the series had explored more with the standard bosses.