#2 Fake-out entrance
Again, it's all about the mind games. The Fiend could make a normal entrance, which would be unexpected based on the advertised match between himself and The Miz, but it could quickly turn into something different. Miz could stand his ground and go face-to-face with The Fiend, only for the lights to fully come on for the big reveal: The Fiend is in front of him, but Bray is behind him! The Fiend simply gestures for Miz to turn around, which he hesitantly does, and there's Bray! The lights go out, The Fiend disappears, and Miz has his match with Bray Wyatt.
Going forward with the possibility of The Fiend and Bray Wyatt not being two separate mindsets of one physical man, but rather two different men entirely can really be explored if WWE goes in that direction. Who is The Fiend? Is Bray Wyatt real? Was he ever real? Is The Fiend a higher power that Bray looks up to, who uses Bray as a puppet to throw people off the scent of him being a completely different person altogether?
A top AEW star just called one of his colleagues 'spoiled' and 'narcissistic' HERE.
That may be taking it a bit far, but the idea of The Fiend and Bray Wyatt, two minds inside of one body, being able to not only mentally but actually physically exist in the same place at the same time would be absolutely horrifying.