If you’re able to collect all 883 Moons in Super Mario Odyssey, here’s what you’ll unlock:
-The Odyssey’s sail will turn gold.
-A new portrait of Bowser will appear in the Wedding Hall.
You can also collect up to 999 Moons — just spend cash at the Crazy Cap shops and buy up all the moons until you hit the maximum amount.
Go back to Princess Peach’s Castle in the Mushroom Kingdom, and you’ll find something new — you can kick off a celebratory fireworks show whenever you want.
Activate the scarecraw to the left of the castle, climb the stairs, then hit the second scarecrow to create a pole. Shimmy up to the top of the huge hat and swing Cappy at the metal piece in the center to start the fireworks show.
Take a trip to the Moon Kingdom and check out the portrait for a surprise. The new portrait is located on the right as you enter, and lets you re-fight Bowser with a twist.
The final battle is far more difficult this time around, and it’s the last possible challenge you can overcome as Mario. What do you get for beating the final challenge in Super Mario Odyssey?
For beating the 100% completion Bowser battle, you’ll get…
A postcard! Yup. Another postcard.
Since Super Mario Sunshine, postcards have been the grand reward for doing everything in the game. Basically, they exist just to say “Thank you!” to the player. If you value your sanity, don’t go nuts hunting all 883 moons hoping for an awesome reward.