This'll be a short one, as this stage consists of a single gimmick. Shooting the lowest cracked walls causes the screen to shake while the stage falls down until the next lowest wall is at the bottom. It works out okay as a visual effect, but as a game mechanic, it's pretty weak. There are no enemies or distractions that might cause us to shoot the wrong walls, special weapons can't hit them so there's no advantage to taking out walls in any order other than lowest to highest, the spikes in the first half are more of a threat than the falling ceiling, and the second half doesn't even pretend to make the player think about it.
The only puzzle to solve, if it can be called one, is that the tight jump with spikes above can be made easier by leaving one block and shooting it out just before jumping, as Mega Man can then make a full jump instead of a short one and run left before the ceiling falls. I'll also give it credit for the spikes between the second and third pillars, as it is very tempting to try to jump and shoot them all immediately.
It's a shame Mega Man doesn't start all the way to the left, as that could also lead to a gotcha death if players try to jump and shoot the first pillar before they see the spikes.
We get a little cutscene here with a fake Proto Man incapacitating Mega Man in one shot before Real Proto Man reveals him as the last Dark Man. He uses shots from the first, the shield from the second, and from the third he takes... jumping, I guess? His only moves are to fire three shots (he seems to have lost whatever he nearly killed Mega Man with) or extend the shield out and jump.
The shots are close enough together to make dodging them difficult, and the shield has to be jumped twice each time he uses it, but I still find this easier than Dark Man 1 or 3. He can only move by jumping, and it's a big, slow jump that leaves him open. The shots are also high enough to slide under, which is a little easier than trying to jump them. He takes two damage from Power Stone and Star Crash, so just ignore that and hit him with charge shots or Beat, who can still attack through the shield.
I can't say much about this one. The stage mechanic can be interesting but the game doesn't go anywhere with it and was clearly just using it as a set piece before throwing us into the boss fight. The boss spends half the battle throwing his shield away, and the most interesting thing about him is that the spacing between his shots hits some kind of sweet spot for annoyance. There's just barely enough time to jump between them without also moving backwards, or to jump over two of them at once, but trying either is extremely dangerous. It's best to jump backward, or makes a series of quick slides forward, or any combination of the two.