#4 Elias wins it clean
This might be the least likely finish due to WWE's reluctance to give anyone a clean win over their Supermen. Prior to the last few years, a clean win over John Cena used to be a huge deal. Now that he's a part-timer, it isn't such a big deal when Cena loses.
That treatment has been transferred to the newest 'Golden Boy' in Reigns. He really only loses when the circumstances are so insane like a beat-down by five opponents or he is defeated in a match where a pin-fall isn't the only way to win (Ambulance Match, Table Match, Ladder Match).
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When someone new defeats the chosen Superstars, it's a big deal. Kevin Owens defeating John Cena initially presented him as a huge deal and someone to be taken seriously. If Elias somehow gets a clean win over Reigns, it would be huge.
It would give 'the Drifter' some credibility as a player in the main event and it would also give him a legitimate claim to be one of the next challengers for the WWE Championship.
It would also show that Reigns has some vulnerability which would be understandable after his last year or so. This type of finish would also be new and refreshing in the WWE, so they likely won't do it.