Culex

Culex is an optional boss in Super Mario RPG: Legend of the Seven Stars and is considerably the hardest enemy in the entire game. He claims to be a dark knight from the alternate dimension known as Vanda.

He is accompanied by 4 crystals, one for each element of nature (hinted by their powers; Red=Fire, Yellow=Earth, etc) which makes him harder to defeat. He and his crystals make up a total of 12,396 hit points (HP), the highest in the game. He possess some the strongest moves in the game, so Peach (the healer) is highly recommended for this fight. He is one of the few bosses in the game to have a strategy beforehand to face him. After defeating him, he will congratulate you in your victory by calling you a champion and reward you a keepsake for your fight with him with the Quartz Charm, one of the most useful items in the game.

Trivia

 * He was designed by Square Enix and makes a reference to the Final Fantasy series ("Perhaps in another game, another place, we would have been mortal enemies") after defeating him. His music is also the boss theme of Final Fantasy IV.
 * Culex's base hit points, 4096, is the square of 64.
 * Culex shares his name with a genus of mosquito.