Mega Man 3/Wily Fortress 4

A short and pretty simple level. You'll fight through a few small corridors, with the only threats being deformed rock robots that heave boulders at you. These guys aren't too hard to take out, and don't pose a threat at all. Just blow them away and keep moving forward.

There's no real "boss" in this level, but instead you must fight all eight robot masters again in a teleporting hatch room. A useful piece of advice - each Robot Master is vulnerable to his own weapon. Use this strategy if you get low on the "traditional" weakness.

Once all the Robot Masters bite the dust, step through the door at the bottom-right hand corner of the room, and exit via the teleporting hatch.