Mega Man 2/Wily Fortress 2

There are a lot of spikes in the second stage, so you'll find yourself using the Items to avoid them quite a bit. Just be careful, watching your step as you progress through the stage, and you should be all right. Remember, a Crash Bomb can destroy hard walls your Arm Cannon will bounce off of. This is useful for getting some items in the stage you otherwise wouldn't be able to reach.

At the end of the stage you'll find yourself in a small room, in which chunks of the wall combine together into small but deadly robots. They aren't vulnerable until they combine, so don't fire until then. There are two main strategies to employ here:

1) Bubble Lead. Very hard to hit with, but it will kill each robot in a single shot.

2) Metal Blade. Not as powerful as Bubble Lead, but you can aim in any of eight directions, making it a much easier weapon to hit the bots with.