Mega Man 4/Wily Fortress 2
This level is another of the "obstacle course" variety, with plenty of spikes and difficult routes to challenge you. Fortunately, there's really nothing new here you have to know about. Just stick it out and keep moving forward. You'll reach the boss before long.
At the end, you'll encounter a giant bomb ball machine. There are two lifts in the room, and the giant robot (who occupies the entire right side of the room.) He'll try attacking you with fireballs and bombs, but his weak spot, the green dot on his head, is painfully obvious. Using the lifts, fire away at his weakness. Ring Boomerang is his weakness, but due to the limited range, you may want to opt for using your regular weapon.