https://www.gamespot.com/articles/free-super-mario-odyssey-dlc-update-revealed-for-n/1100-6456022/

During the surprise Nintendo Direct Mini this morning, Nintendo announced that Super Mario Odyssey is receiving a free update in February with new items and opportunities to compete with other players online. Once the update is released, players who have completed the story mode can look forward to a new mode called Balloon World.

This area can be entered by talking to Luigi atop a skyscraper in New Donk City. Balloon World lets you hide balloons within stages that other players must race to find, and conversely, you can compete while racing to find other balloons hidden by players from across the globe--everyone's performances are ranked online.