It will be a nightmare if you are not so good at these weapons & bosses, especially those giving red/purple keys :(
There are 3 ways to get huge damage to bosses in the level: charge your weapons (oil slider and mega ball included), hit bosses more at one time by using weapons producing multi bullets, fire earlier to make sure more bullets can hit bosses when their invincibility frames disappear(you will need the last tip when meeting burst man & bubble man)