Mega Man 2/Wily Fortress 3

The third stage is short and simple, just don't accidentally get yourself killed.

In the first section, giant metal fish leap out from pits in the watery section, trying to knock you to your death. Don't try destroying them, it won't do any good (unless you use the crush cannon.) Just wait for them to come up and descend, and once they've descended, continue on your way.

In the next section you'll find yourself falling down spike-lined chambers. Simply move as the screen scrolls, avoiding the spikes. The spikes are, of course, instant death, but they're not that hard to avoid really.

The boss of the level is Guts Man of Mega Man I fame. But he's been rebuilt as a HUGE bulldozer. The funny part? He's even easier than he was in Mega Man I!

Just jump in the front of the dozer, and unload on his face with Quick Boomerangs. You can kill the guy before he has a chance to attack!