The bosses I always felt were very cool

You will encounter on average 1-2 sub bosses a stage as well as a main boss

(At the eighth each big boss comes back and you must defeat Mr. X!)

Great music, great attention to detail, a semi-sophisticated fighting system, weapons, tough bosses, and a varied assortment of fighters and fighting styles all packaged neatly together in one game makes this the gold standard of side scroller beat 'em ups

Also, the robots Oxygen and Nitrogen are fun to fight, and my personal favorite was the boss of the boat, a giant bald boxer named Bear