The product is an expansion for Arkham Horror: The Card Game. There is no option to play separately with only the add-on, the main game is required.
All major new expansions for Arkham Horror: The Card Game included card decks for new investigators, but you have the chance to add additional investigators to your collection.
In the Nathaniel Cho Investigator Deck, you'll find a complete, game-ready investigator deck. In order to join an ongoing or a new Arkham Horror campaign, you no longer need to buy another Core set or expansion, you can join with this deck as well.
Veterans of the game may also want to purchase this deck, as the cards it contains offer new ways to play and can add variety to your Arkham Horror card collection.