Mega Man/Wily Fortress 4

Here you are, the final stage of Mega Man I.

Start the stage by heading upwards, avoiding the Watchers and destroying them when the opportunity presents itself.

You'll encounter a dangerous lift, like you found a set of in the Guts Man stage. This one has an even bigger "broken" section that will plummet you to a spiky death, so just use the Magnet Beam here.

At the end of the corridor is a hard-to-reach Yashichi (a Category:Capcom trademark in the old days), which will restore your life and weapon energy.

You then enter a linear set of teleporters in which you fight the robot masters again (apart from the two you fought in Stage Two) in this order: They're all weak to the same stuff as before, so bring the pain.
 * 1) Bomb Man
 * 2) Fire Man
 * 3) Ice Man
 * 4) Guts Man

Once you're through here, head down the hallway to meet the final boss: Dr. Wily.

The battle begins with Wily flying his saucer into a large contraption, with a large pink cannon at its base. This is a two-part fight. To win Part One, equip the Fire Storm, stand by the cannon, and let the flames fly. It's more effective if you stand by the cannon, and let the fire around you hit the cannon. Its energy will run out very quickly.

And then comes Part Two, the more difficult section of the fight. With Wily's face exposed and the cannon gone, a jewel is visible below the cockpit. You'll want to use the pause/resume trick with the Thunder Beam on the jewel (the contraption's only weakness). Dodge the shots he fires, and you should fare all right.

Congratulations, you've beaten Mega Man I!