Ever since Wario stuffed the Black Jewel back into it's chest, it has tried to escape. Wario decided to throw a party because he got all his stuff back.He invited the whole gang. They partied so hard in knocked over the chest holding the Black Jewel. After the Black Jewel escapes, it turned Wario's castle into a new world, sucking Wario, and his friends into the new world.
Each of Wario's buddies can help him through his journey to defeat the Black Jewel.