#4 Heel Turn - Finn Balor
Face Finn Balor hasn't run its course, but with the reluctance to ever let him have another run as either WWE or Universal Champion, his options are limited. He has had two runs with the Intercontinental Championship but those were short-lived. His "Demon" persona comes out when he needs to close a feud out with a slam-dunk win, but even that's an aspect of his character that needs a slight change.
There have been rumblings of Balor joining the Club sometime in the near future and if he did, he would obviously be a heel. That side of his character has yet to be explored and it is something that could propel him to the next level.
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If he still uses "the Demon" as a heel, it could be used as a vicious and relentless visage rather than a painted guy who crawls to the ring. Balor already has the in-ring skill, but sometimes character work and tweaks give stars better shots at greater glory. If the Club is supposed to be taken seriously, adding Balor would help but he needs a dangerous edge to solidify that.