Participating U.S. Burger King locations will offer a “BOGO Wednesday’s Whopper” deal to rewards members on Thursday, October 17, which happens to be the day an October supermoon will peak.

The offer, aptly marketed as Uncle Fester’s Full Moon Feast, is valid while supplies last, and purple buns are not guaranteed.

You’ll need to buy one full-priced Whopper to score the deal

Rewards members who purchase a Wednesday’s Whopper at regular price on October 17 will get another one free. The limited-edition menu item is basically a traditional Whopper, but served on a purple bun that gets its color from purple potatoes.

Certain exclusions apply

The BOGO deal is only valid on the Burger King app and website for pre-order or dine-in. Rewards members can use the six-digit ‘My Code’ located in their rewards account (if available) and activate the offer in the ‘Offers’ tab to score the deal.

As always, price and participation may vary and larger sizes/customizations may incur additional costs.

Rewards members are limited to one offer per account and the deal cannot be combined with other coupons or offers.

Finally, the offer is not valid in Alaska, Hawaii and the US Territories, and is not available during breakfast hours.

The new Addams Family menu contains four items

Each of the items in the limited edition menu is inspired by the animated film ‘The Addams Family’.

• Wednesday’s Whopper: A Whopper with Swiss cheese, tomatoes, lettuce, mayonnaise, ketchup, pickles and onions on a purple bun.
• Thing is rings: Crispy onion rings with themed packaging.
• Gomez’s Churro Fries: Crispy fried churros covered with cinnamon sugar and served with chocolate dipping sauce.
• Morticia’s Kooky Chocolate Shake: A shake made with soft serve ice cream, chocolate cake batter fudge, and black and purple cookie pieces.

Burger King also has a King Jr. collection. Limited edition meal toys to celebrate the new menu.