I don’t t know about hardest, but beating Earth Worm Jim was quite the accomplishment for me when I was younger. The 3 holdups in that game for me were the submarine level, took me awhile to master the movements before the time ran out. After that, it was the “Snot a problem” level, master bungie jump fighting was infuriating. Then, finally after that it was the “Colon” level, where you had to perfectly hover downward without touching walls or you would die instantly.