In most RPG games(Final Fantasy or Kingdom Hearts, for example) or otherwise, an enemy who usually has nothing to do with the story but when fought is usually much more difficult to defeat than that game's actual final boss. These enemies also usually present rewards to those who are able to defeat them in battle. Most are notorious for being a massive headache to beat.
Emerald Weapon in Final Fantasy VII and Vanitas Remnant in Kingdom Hearts: Birth by Sleep are both Secret Bosses.
by Shadow0113 February 27, 2011