You guys have not tried 'hard bosses' till you've played...

Earth Worm Jim (Mega Drive) - Killing Queen Slug-for-a-Butt.

Its impossible if you try it normally and JUST possible if you cheat. In all honesty, NOTHING in my library of games beats how hard she was...it was so hard I still remember fighting her for the first time. Had 7 lives. Died in 3 or so minutes. Cheating with 99 lives took me 25 minutes to kill her and I had lost about 70 lives.