Avengers: Infinity War - Every Character Confirmed So Far

Confirmed By: Dave Bautista confirmed he's involved, though doesn't have a script yet (on Twitter), but it was screen-writer Christopher Markus who first dropped the most serious hints to The Verge that Drax and his fellow Guardians would appear:

Also, whether they’re a 12-foot purple guy, or a raccoon, or an android, they’re all people, and we’re going to write them as people. You can’t write them any other way. So, ideally it will stay grounded because you’ll completely understand why the characters are doing what they’re doing, and you will in some way or another empathize.

Plot Predictions: He's one of the most dangerous members of the Avengers/Guardians alliance, so expect him to either be heavily involved in the violent set-pieces of the war, or to be taken out early by Thanos when he gets his hands on the Stones.

Plus, he has unfinished business with Thanos, as he stated in the first Guardians movie...

Gamora: "Your wife and child shall rest well, knowing that you have avenged them."Drax: "Yes. Of course Ronan was only a puppet. It's really Thanos that I need to kill."

Knowing the Russos, his role will be as similarly heavy on humour as it looks to be in Guardians Of The Galaxy Vol 2, as well.