#1 Dean Ambrose

Dean Ambrose has been out of action since December 2017 after suffering a triceps injury during a match on Raw.
WWE announced that Ambrose would be out of action for no less than nine months until the point that he recoups from his injury.
Did you know a top WWE Superstar just wrestled outside the company? More details HERE
But we know that WWE is known to exaggerate injuries to facilitate a surprise return in the future.
If that might be the case for Ambrose, then the greatest royal rumble match could be the perfect place for the Lunatic Fringe to make his return.
Ambrose was initially planned to be Seth Rollins' opponent for WrestleMania 34 before his injury. But that feud could materialise if Ambrose returns at the Greatest Royal Rumble.