Rigor Mortex

Rigor Mortex is a superboss in Dragon Quest Monsters Joker 2, the main antagonist of said game and the source of most of the conflicts that torment the inhabitants of The Island.

Backstory
It was the creation of a madman named Zelham as an attempt to gain control of The Island from the tribe he rivaled, who had Leonyx as their leader. While it managed to corrupt Leonyx's soul, the machine also consumed its creator. Also Leonyx managed to save his heart by turning it into a Sanguini and sending it away, his soul was still posessed.

Rigor Mortex is a three-spaced giant monster and easily the hardest boss in the game. It's also the hardest to synthesize as it requires a Leonyx and a Zenith Dragon, both of which require monsters that at one point required a Captain Crow. This makes it impossible to get with just one game card.

Trivia

 * The monster's name is based of the word "rigor mortis". Possibly a portmanteau with "Rolex" or "Libranex", its japanese name.