Mega Man 2/Wily Fortress 6

After destroying Dr. Wily's ship, the floor beneath Mega Man's feet will explode, causing him to plunge into darkness. When the next stage begins, you will be in free fall. The road to the final battle is short and contains no enemies, but it does have a particularly dangerous hazard that must be avoided at all costs. Red acid drips from the ceilings of the cavern that you must run through, and it's quite harmful to Mega Man. However, there's an unintuitive trick that you can employ to avoid the danger


 * A: Your instincts will tell you to remain in the center of the screen where you risk the least amount of danger from any potential traps that might appear from either side of you. However, in this case you should ignore those instincts, and push Mega Man as far to the right as possible while he continues to fall.


 * B: You must now run through a tunnel cut into the rock beneath Wily's fortress. As you proceed that tunnel will continue to get narrower.  All the while, red acidic substance will drip from the ceiling.  This substance will do a lot of harm to Mega Man if any of it gets on him.  However, if you heeded the advice above and pushed over to the right, then Mega Man is far less likely to get dripped on, as long as you proceed to the right and never double back to the left.  There are no other threats and nothing to collect, so simply run to the right until you reach the door that leads to the final confrontation with Wily,

Boss: Alien
Upon entering this room, the lights will dim and Dr. Wily's saucer will fly on to the screen. He will hop out of it, float in mid-air for a bit, and transform into an alien lifeform. This lifeform will begin floating around the room along a path that resembles an infinity symbol (∞). All the while, he will shoot at your current location.

If you try every weapon against him, you will discover that nothing will damage him besides the Bubble Lead. Even the Mega Buster is useless. For this reason, it's important that you have a good supply of Bubble Lead ammunition available when you reach this room. If you don't, or if you run out of Bubble Lead, you will be force to die until you can continue your game, at which point all of your weapons are replenished.

Because the lifeform spends a good portion of this battle near the top of the ceiling, he lies out of your weapon's reach until he sinks back down to the ground. It is at these moments when you must close in, jump into the air, and drop a Bubble Lead on him. All the while you must make sure that you don't jump into him, and that you avoid his shots as best as possible. It will take 14 Bubble Leads to defeat Dr. Wily, so be patient and time your shots well. Use up any remaining E-Tanks as necessary. Once he is defeated, you will be presented with the game ending, and the staff credits. Congratulations!