You're getting very close to the anticipated showdown with Protoman now, but you'll have to get through one more lengthy and challenging stage and boss before you'll have your shot at the master of the manor.
Start right from the entrance after preparing a charge shot, as you'll almost immediately come across one of the purple knights in a flying orange pod. Shoot him down before he can ram you, and keep going to encounter more of his kind. You have to proceed along a series of ledges, also dealing with the construction cones that like to slide toward you as you approach. It's hard to avoid taking damage here, but charge shots should keep your enemies at bay so you can reach the ladder and ascend into an overhead chamber.
Here, you will find a few of the bulb enemies that drop from the ceiling, as well as an energy capsule. Take care of the foes and grab the energy in the likely event that you need it (you'll have to use Rush Coil to reach the ledge where it rests), then ascend another ladder.
Here, you are greeted by one of the shielded turrets, along with three armored bats. Let them start down from the ceiling, then head left from the top of the ladder and turn to face them. You can take them out with charged shots before they ever get close, and you should have enough time to easily avoid any bullets headed your way. Then you can take out the turret and head through an opening to the right.
In this room, there are a few floating enemies that you can take out easily enough, and then you'll need to use the glowing ledges to reach the ladder. When you jump on the lowest one, it will fly toward the side, and you need to jump from it to the next one when the time is right. If you wait too long, you'll be carried into spikes along the wall. From the second platform, you should then jump to a ladder and climb it before you meet with another set of spikes.
The overhead chamber that you'll reach from the top of that ladder basically repeats the process, only with a few additional spikes that shouldn't even prove relevant. If you mess up and the ledges fall without allowing you to reach the next ladder, you can descend briefly to the previous room and then ascend once more to try again.
Once you do successfully reach the next screen, you'll find that you can advance toward the right, through an area that looks a lot like Star Man's stage did. Here, you'll need to jump along platforms where hardhats are positioned on turrets. Take care of them with charged shots (you can move close enough to make them try to fire shots at you without risking any treacherous jumps) and continue advancing along a series of ledges. There are a few flying enemies here, as well, so be careful.
At the far side of that area, you can climb a ladder to an overhead room and defeat a green enemy that drops from the ceiling, before using Rush Coil to reach another ladder that you can ascend.
In the next area, you'll start to the right and spot a snake of blocks that emerges from the pit. You need to hop onto it and ride it toward the right while it negotiates a series of platforms. This isn't especially difficult, provided you stay near the front half of the makeshift vehicle. You'll pass a series of ledges with an extra life and an E-Tank, and you'll have to deal with quite a few spikes as flying enemies try to knock you into the abyss. Of course, they could actually wind up helping you, if they inflict damage that allows you to brush against spikes without losing a life. You should develop a feel for the situation, and it shouldn't be especially difficult to reach the far side. The Rush Jet can also help with that, in a pinch.
When you reach the far side of the area, you can start down a ladder into a lower room. It's a good idea to simply drop from the ladder and into the next room. Then you should be ready to head quickly left, in time to slide under a large pink robot that will leap toward you. Don't even stick around and try to kill him. After you slide under him, just keep moving and drop into the gap on the screen's left side.
On the next screen, you're greeted by another of the pink brutes, and this one you'll want to eliminate swiftly as you head cautiously toward the right. You will find a pit in that direction, with a shielded turret on the opposite side. Take it out with a charged shot when it raises its protective plate, and do the same to a few more as you ascend to a ladder.
The ladder leads to a room with another of the pink fellows, and there's not a lot of room to avoid him. You could always use Beat while you cling like a coward to the ladder, and honestly that's probably not a bad idea. Then when the path is clear, you can head left and drop down to a ledge for an easy E-Tank.
Next, climb the overhead ladder into the next area. Here, you'll have to ride another of the block snakes across a starry sky. Along the way, you'll encounter some of the suicidal enemies that attacked you on the bridge in Gyro Man's stage. They should fall ahead of you and not pose much of a threat, as long as you're riding wisely. When you reach the far side of the expanse, you'll be able to enter a gate to deal with another of the castle's guardians.
Your enemy this time doesn't look a lot different from the other bosses that you've already encountered in the castle, except he's purple and one of his arms is a large cannon.
As the fight begins, he'll leap toward you and let out a stream of bullets that hopefully you can dodge. They travel in a diagonal line and should land at your feet, so jumping over them isn't overly difficult. That move is followed up by a spread shot that flies in your general direction at the time the shot is fired, so you might avoid it just by jumping around a lot. If it does catch you, it'll freeze you into place for long enough that you're likely to get shot or bumped into before you thaw.
Now the battle can begin in earnest, and you'll want to start by distancing yourself from your foe with a few quick slides while he fires more bursts from his cannon. Then switch to your Gryo Blades weapon. You can use it to attack from a reasonable distance, which should give you more time to avoid your foe's shots. You have to hit him quite a few times, which means a lengthy battle, so it's likely you'll need to resort to using an E-Tank before it all concludes. You may also have to finish off your adversary with your arm cannon, if too many of your shots go wild.
Sometimes, the boss will walk toward you along the bottom of the screen, and in that case you can spam a few attacks before he tries a new tactic. Take advantage of such moments to reduce the length of the battle and you should do just fine.
NEXT: Stage Four