Fire Storm

Fire Storm is Fire Man's power. Fire Storm does double duty--it shoots a fireball, and has a shield effect (albeit for a brief moment). So for the first part of the Wily Battle, you can use Fire Storm to both use the initial fire ball and the shield to do some damage. The Fire Storm is also perfect to make short work of Bomb Man, in Mega Man, at least. The Mega Man: Powered Up version is better against Oil Man.