Galaxy Man - Use Mega Buster
Jewel Man - Use Black Hole Bomb
Plug Man - Use Jewel Satellite
Tornado Man - Use Plug Ball
Magma Man - Use Tornado Blow
Hornet Man - Use Magma Bazooka
Splash Woman - Use Hornet Chaser
Concrete Man - Use Laser Trident

Wall Shooters - Use Mega Buster
Giant Machine - Use Laser Trident*
Blob Monster - Use Black Hole Bomb
Dr. Wily #1 - Use Mega Buster
Dr. Wily #2 - Use Mega Buster
Dr. Wily #3 - Use Plug Ball**

* - The Laser Trident is the weakness of all three sections of this boss, but the middle section is made much, much easier by using the Tornado Blow on it.

** - The Plug Ball is the primary weakness of Wily's final form (the UFO). However, if he appears too high to attack with the Plug Ball, quickly switch over to the Hornet Chaser and use it on him. They will hit him high above for only one bar of energy per strike, but it will help you decrease his energy a little bit more.