It arrives as part of the game's expansion pass - available to buy from the Switch eShop for $19.99 / £17.99 - and adds four more X-Men and an all-new Danger Room mode. Here's some more info from Nintendo's website:
DLC Pack 2 – X-Men: Rise of the Phoenix (December 23rd, 2019)
Dark Phoenix, the infinitely powerful cosmic entity from one of the X-Men's greatest sagas, unleashes an era of fiery destruction! Four more X-Men join the alliance – Phoenix, Gambit, Ice Man, and Cable – with the purchase of the MARVEL ULTIMATE ALLIANCE 3: The Black Order Expansion Pass.
Face-off against friends in the newly added Danger Room mode! Up to four players will compete to see who can take down the most bosses while being barraged by buffs and debuffs.
A third DLC pack has also been promised at some stage, although its release date and contents are currently unknown.
Will you be getting stuck into this X-Men: Rise of the Phoenix DLC today? Let us know with a comment below.