#1 He could encourage Seth Rollins and give him advice

Seth Rollins has arguably the biggest match of his career ahead of him at WrestleMania when he stands across the ring from 'The Beast Incarnate' who will be the only thing standing in the way of him and the WWE Universal Title.
Someone who knows all about standing across the ring from Brock Lesnar at WrestleMania is Roman Reigns, who also happens to be Rollins' close friend and stable-mate, meaning that a fairly obvious thing for Reigns to do at Raw is to echo Dean Ambrose's sentiments and encourage Rollins to 'slay the Beast'.
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Hell, imagine the atmosphere if Reigns was to go as far as to tell Rollins that when he does beat Lesnar, that 'The Big Dog' will be next in line!