Black Jewel

Black Jewel: "I'm going to take my guardians in Treasure Square of different Levels!"

-The Black Jewel rises up in the Treasure

Black Jewel (also kown as Rambregs the Evil Black Jewel) is a treasure that Wario collected prior to the events of the game Wario World and he's mentioned in Fortune Street, and it also serves as the final boss of the game.

Wario World
Black Jewel: "DIE!"

-The Black Jewel takes Wario fell down in the Treasure Square flour

Black Jewel makes first appeared in this game, one of Wario kills the Black Jewel's 12 guardians and Wario is going to kill the evil Black Jewel.

Fortune Street
Wario: "The big treasure is in this place is a wand, huh? Guess a silly stick is better than a Black Jewel!"

-Wario in the kingdom of Trodain

The Black Jewel is mentioned by Wario on a Castle Trodain level of Fortune Street.

Names in Other Languadges
English : Kevin Smith

Spanish : Joya Oscura

French : Joyau Noir malfaisant

German : Dunkles Juwel

Trivia

 * Allthough the evil Black Jewel does not appear in Fortune Street, i think he's mentioned by Wario where Wario said "The big treasure is in this place is a wand, huh? Guess a silly stick is better than a Black Jewel!"
 * There's some Wario World videos on Youtube during the battle in different Years of the months.