UPDATE 17/10/17 5.10pm: Mario and Rabbids: Kingdom Battle's first big season pass update is now official, and Ubisoft has released a proper launch trailer to mark its arrival.
ORIGINAL STORY 16/10/17 8.25pm: Mario and Rabbids: Kingdom Battle has, somewhat unexpectedly, received the first of its two promised larger-scale season pass content updates today, in the form of new single-player challenges and a co-op campaign.
The season pass was revealed prior to Mario and Rabbids: Kingdom Battle's release, and two minor weapons packs - the Pixel Pack and Steampunk Pack, each featuring 8 specially themed weapons - are already available. However, word on the season pass' two, more significant updates - featuring "new solo challenges", "new co-op campaign", and "new story content" - has remained vague.
Earlier today though, Reddit users began to report that receipts for season pass purchases on Nintendo's eShop now included release dates for the two major Mario and Rabbits DLC drops - the first due tomorrow, October 17th, and the second on January 16th, 2018.
In actuality, the first of these updates appears to have released already, although you might need to manually update your game in order to receive it. NintendoLife reports that the update is called the Ultra Challenge Pack, and features new single-player "Special Challenges" and the "Cataclysm Kerfuffle' co-op campaign.
Special Challenges are accessed from the Secret Areas in each of the four worlds. Cataclysm Kerfuffle, meanwhile, offers five co-op maps and unlockable 'hard mode' versions.
Ubisoft has yet to officially confirm the launch date for Mario and Rabbids' second, story-focussed DLC pack, but there seems little reason to doubt the veracity of those January 16th 2018 reports after today.