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! When you first begin to fall, hug the right wall. The second you land, start making your way through the stage. If you don't stop, the acid won't be able to catch up to you, and you won't get hit!

Boss
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 an "infinity"-symbol pattern (a transversal 8), firing shots as he does so. He is only vulnerable to Bubble Lead. Don't touch his body, or you'll lose a lot of hit points. Just keep using the Bubble Lead and being careful, and you'll win without much trouble.

Ending
After beating him, Dr. Wily's 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!