Avengers: Infinity War - Every Character Confirmed So Far

Confirmed By: The ever-enthusiastic talker Vin Diesel, who spoke to Screen Rant about his new sequel xXx: Return of Xander Cage, and basically confirmed he's involved in Infinity War:

And in Infinity War, I have to talk to the Russo brothers and find out how this is all gonna go down. I know somewhere in the Marvel universe there is a moment when you will see Groot and Hulk have a few words. I think there's gonna be a moment that we're all waiting for, and whether you know it or not, you are waiting to see Groot and the Hulk get down.

Plot Predictions: The size issue will be an interesting question, as Baby Groot would be a lot less useful in the fight against Thanos than the full grown monster, but he's clearly not as cute and if Guardians of The Galaxy Vol 2 establishes him as the MVP of Phase 3 (in merchandising sales at least), Marvel will surely be reluctant to super-size him again.

One thing's for certain, though - while Vin Diesel wants it to happen, Groot probably won't be fighting Hulk, unless through a case of mistaken identity?