#4 Special guest referee
Another way WWE can raise the stakes in this match is by introducing a special guest referee into the mix. Not only could a special guest referee help create doubt as to who will ultimately come out on top in the main event contest, it will also allow WWE a variety of options when it comes to the end of the match.
For example, if WWE introduced Triple H or Stephanie McMahon as a special guest referee, it would allow for Reigns to be screwed out of the victory without hurting him with a clean pin. If WWE wanted to do the opposite, they could screw over Lesnar by aiding Reigns in winning the championship, which would protect Lesnar from a clean loss as well.
This of course would be used as a way to take the sting out of a loss for either superstar and also keeps them booked strong after WrestleMania 34. Then again, WWE could really switch things up by having Paul Heyman be the special guest referee, which would be a huge swerve for fans, and allow Lesnar to be pinned without losing momentum.