#4 Kane
The Big Red Machine has been away from the ring for more than a year after making the switch into politics and winning the race to become Mayor of Knox County in Tennessee, but Kane returned to SmackDown last week and The Fiend decided that the two men still had unfinished business.
Kane is someone who used to strike fear into the hearts of many WWE Superstars and now he is an afterthought. If Kane wants to make a statement against The Fiend then surely the best one would be to be part of the Royal Rumble and attempt to win it so that he can then bow out at WrestleMania 36 in a passing of the torch match.
It could even be made a mask vs mask match if WWE felt the need to make the match even more of a spectacle, but pitching the match as Kane's final one in a WWE ring should be enough to see him want to return for The Rumble and find a way to step back into a feud with The Fiend.