The next upcoming expansion to Marvel Legendary is "The New Mutants". This refers to a group of X-men, who has previously appeared in Legendary as special bystanders in the X-Men expansion.
New Mutants members Magik and Cannonball have already appeared in the game as playable characters in Secret Wars, Vol. 1 expansion and the X-Men expansion respectively, so our guess is that we can rule those heroes out. This is probably going to be a 100-card set, given the material.
With that in mind, here are our speculations:
The next expansion in line for the Marvel: Legendary series is Heroes of Asgard
This expansion will come out on February 26th, 2020 and will mark the 20th expansion to the game, which is pretty crazy.
Another Marvel Legendary expansion is on the horizon, with a focus on S.H.I.E.L.D. It's a small set with 100 cards and it will feature new heroes, masterminds, villain groups, etc. Perhaps the biggest news is the special S.H.I.E.L.D. officers to mix in with Maria Hill.
Another expansion for the successfull Marvel: Legendary series is coming out in August. This time, we will have heroes like Scarlet Witch, Quicksilver and War Machine joining our ranks to battle the mastermind The Hood, among others. The set will also feature the Mandarin, which looks like a really cool Mastermind with some fresh ideas. When it comes to villain groups, the set will feature cool villains like the Dark Avengers.
Another expansion for Marvel Legendary is due in May! It's a small expansion, as in 100 cards, it will contain a new keyword, Switcheroo, and two returning ones, Investigate and Teleport from Noir and Dark City/Secret Wars respectively.
As the previous small expansions, there will be 5 new heroes, 2 new henchman groups, but only one new mastermind, to make room for 5 new bystanders.
Another franchise has joined the Upper Deck's Legendary deckbuilding series, after other titles like Aliens, Firefly and Big trouble in little China.
The expansion in a nutshell: