The basis of Jamboree is exactly what its name implied; a fun mix of Pokémon cards. Taking cues from other previously unreleased sets Crosstrainer and the Unnamed Wizards Set, Jamboree was going to have a number of cards Wizards created on their own and other cards never previously released in English from sets like the Vending Machine cards and other promos. Ultimately, Jamboree might have actually brought American and European players up to date with Japanese players, as many Japanese cards have yet to be released in English.
A lot for this set, like promotional material and box and pack designs, were created, finalized and ready to be released. However, Nintendo prevented this set from being released, so it never made it into the hands of players.