The first DLC as part of the Marvel Ultimate Alliance 3: The Black Order season pass will drop on September 30.
Marvel Ultimate Alliance 3 players who purchase the pass can download the first content drop on September 30.
The first expansion is Marvel Knights: Curse of the Vampire and includes playable characters Blade, Moon Knight, Morbius, and The Punisher.
As Nintendo Everything notes, the date on the Nintendo UK website could be a placeholder. That said, the first DLC drop is slated for fall, and the date provided falls within the seasonal time frame.

https://www.vg247.com/2019/07/20/mar...arvel-knights/