If you've played any previous Mega Man games, you're probably expecting what finally happens here: the revival of the initial eight boss robots. You'll have to defeat all of them without continuing if you want your shot at Wily.
The stage begins with easy access to an E-Tank. Grab it if you have room for it, but otherwise leave it where it is and save it in case you lose a life somewhere in the battles ahead and return to this spot with room in your inventory for another tank.
Head right from the starting point and take out a turret with a charged shot, then pass through the teleporter and you'll appear in a room with several additional teleporters positioned around a central platform.
As you pass through each teleporter, you'll face one of the robot masters. Their weaknesses haven't changed, so take advantage of the fact.
Each time you defeat a robot master, you will gain a large energy capsule to keep your health topped off. If you need to, you can also use an E-Tank or two or three, but don't be afraid to lose a life along the way if you need to, rather than using up one of your tanks.
Once you defeat the robot masters, a new portal appears and you can pass through it to take on Wily himself.
This fight can be intimidating at first, especially with a lethal pair of spikes that are positioned along the center of the floor where it takes place, but it's actually quite easy once you get the hang of it.
Wily appears in a large spaceship that moves around as if it has had too much caffeine. You should take up a position along the center of the three columns either to the left of the spikes or to their right. Let the ship hover over you, jittering back and forth for a bit. Then run and jump across the spikes to change sides.
If you time it right, which you should be able to do with just a little bit of practice, the spaceship will come crashing down against the platforms on the side of the spikes that you just recently vacated. You can quickly turn to face it as it does and jump up to unleash a charged shot from your arm cannon.
The rest of the fight will play out in that manner, with you luring the spaceship to your side, waiting for a bit, and then leaving just ahead of its plummet to the ground. Charged shots actually do a fair bit of damage, and it's not difficult to avoid taking damage for most or all of the fight, so you will quite possibly manage to sneak through this fight without even needing to use up any of your finite supplies.
NEXT: Stage Four