I wanted to wait until today to post this. By now, we've received all the clues and hints we're going to get (assuming the reveal is tonight!). Based off what we've learned, here's who I think it could be:
Adam Cole. Whoever the devil is has to be able to keep up with MJF on the mic and he's really the only one who can. I think he's in cahoots with BCG (Remember, Cole was the one to introduce Jay White to AEW, calling him “his friend”) and I’m betting he's had this planned for a long time.
That would make his henchmen Roddy, Taven, Bennett, and either Britt Baker or Wardlow.
Alternate options are: Jack Perry, Roddy Strong, CM Punk, Britt Baker, Samoa Joe, and even MJF himself.