#4 The Demon King
Did you guys know that Finn Balor was the first ever Universal Champion? It happened such a long time ago that I will not blame you if you've forgotten. We recently saw Balor get his contractual rematch for the prized Universal Championship. Unfortunately, he came up short against The Big Dog.
However, there's always a possibility of Balor tapping into his dark side and unleashing the Demon King upon the WWE Universe. This would allow him to come into the match with a distinct advantage, because the character is unbeaten in the main roster thus far. If you remember, The Demon King was victorious against AJ Styles in a dream match last year too.
Will The Demon King be able to stop the onslaught of the big dog to claim the big prize? Yes, because it's a protected character, I can see it happen.