Mega Man 2/Wily Fortress 5

Ahh, the infamous "you have to fight all the Robot Masters again" stage.

You'll start this stage in the Dr. Wily Teleport System room. Beat all the Robot Masters again the same way you did before. Shouldn't be too tough. For a few giggles, try throwing Metal Blades at Metal Man.

Once they're all dead, a ninth teleporting hatch will appear. Go through to fight Wily's contraption.

This battle has two parts, which are both relatively simple and similar. If you have any Crash Bombs left, unload on the machine with them. If you run out, switch to Metal Blades. There are two parts of this fight, but if you keep attacking Wily, you should win.