#4 Braun Strowman
This one is probably a long shot, but he's been starting to run with the big dogs lately and he has been targeting Roman Reigns. There is a very good possibility that Reigns will be leaving the Alamodome with the WWE Universal Championship, so having Strowman win the Rumble match fits in very well with that narrative.
Another speculated Universal Title match for WrestleMania is Chris Jericho vs. Kevin Owens, which would still allow for Reigns vs. Strowman, but to keep it away from the title picture, Reigns needs a WrestleMania without the big title involved.
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A match with Braun Strowman is a big deal without the Universal Title being involved. The United States Championship maybe, but not the Universal Championship.