We aren't quite sure how, but it appears someone has gotten access to an early copy of Super Mario Odyssey, and they are leaking all sorts of game details. They appear to have downloaded the game, which would indicate that they have access to a press copy, be it from NA/EU. They were actively posting screenshots and information on 4chan, which would be against the game's embargo.
The only other explanations are that they somehow gained access to a legitimate retail code, or manipulated the eShop servers in some way to get access. As of right now, the thread had been archived and the leak has been stopped, but please be careful out there. Thanks to Zippo for the heads up.