Squirreled away in a secret room within Monstro Town, a cliffside hamlet in Super Mario RPG, there's a purple-skinned warrior named Culex. You can go the whole game without ever meeting this man; finding him requires you to backtrack to an earlier town, purchase a pricey set of fireworks, and trade it to an NPC for a crystal that opens the door to his lair. Once you do find the enigmatic knight, he challenges you to a duel. Accept the offer and you'll have to face down a boss more challenging than any other in the game.