Mega Man 2/Wily Fortress 6

You've made it to the final stage of Mega Man II!

There are no enemies in this stage, just acid that drips from the ceiling. Avoid it and make your way to the boss door. The acid hurts bad, so don't let it hit you!

As soon as you enter the boss room, Dr. Wily's flying saucer will fly to the bottom of the screen, and Dr. Wily will float in the middle, then transforming into an alien! He moves in a figure-eight pattern, firing shots as he does so. He is only vulnerable to Bubble Lead. Don't touch his body, or you'll lose a ton of life. Just keep using the Bubble Lead and being careful, and you'll win without much trouble.

After beating him, his holographic projector will break, revealing the real Dr. Wily behind a machine, and he, as usual, will beg for mercy.

You've beaten Mega Man II!