We've probably all had a boss in a game that felt impossible, but what about those bosses that were so well hidden and difficult at the some times, you sometimes didn't even believe it could be real until it kicked your ass a dozen times in a row?
Soul Calibur III's Night Terror was that boss for me, what about you guys? You don't have to watch all the video, but i did just to reminisce on the enemy's power back then.
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Whether or not it technically counts, the Creator ghost in F-Zero GX made me rage. It's not the time trial ghost that you have to beat that makes it hard; you can actually beat it without boosting once, it's the lack of guard rails on the entire track and all the sharp turns that made it so hard.