Mega Man 2/Bubble Man

Stage
Everything about this stage is water-themed. In fact, most of the stage takes place underwater. The Metal Blade is extremely useful in this stage. At the beginning, Mega Man must jump across platforms while being attacked by mechanical frogs. Damage dealt by these frogs can cause Mega Man to fall off the platforms to his death, so it's a good idea to make short work of them with the Metal Blade. Also, there are some platforms that fall as soon as Mega Man jumps onto them, which can be a little tricky to survive. Just move across them as quickly as possible by jumping off as soon as Mega Man lands.

Next, the stage moves on to the underwater portion. Mega Man's bouyancy allows him to jump extra high and extra fast, which can be useful but allows easy contact with the spikes located on the ceiling, so watch out. There are a couple of giant angler fish which attack by spitting out mechanical shrimp. The shrimp are easily defeated with the Metal Blade, but that weapon has a tendency to miss the weak point on the fish (which is the lantern hanging from its head) so switching to the plasma gun might be useful for them. Also underwater is a region with dense spikes and robots which attack by drifting down from above, and then arcing towards Mega Man. Again, the Metal Blade is useful here because of its multidirectional aim.

After the underwater portion, there is another short segment of platform jumping while robot crabs fall from the sky. This can be deadly if a crab happens to fall while Mega Man is in midair between platforms, as it can cause him to fall to his death. With quick reflexes and by firing the Metal Blade upwards while jumping, this portion can be safely passed. After the raining crabs, it's onward to the fight with Bubble Man.

Robot Master
The fight takes place underwater, so the bouyant effect is in place. Just as before, watch out for the spikes in the ceiling. Bubble Man swims slowly around the room while firing his Bubble Lead at Mega Man. Here, the multidirectional use of the Metal Blade is again handy, as it allows Mega Man to fire at Bubble Man without the need to jump, which reduces the threat from the spikes. A few hits from the Metal Blade and Bubble Man is history. His defeat awards Mega Man with the Bubble Lead, which rolls along the ground until it hits an enemy or an obstacle.