#4 Kevin Owens & Sami Zayn

The truth is, we've already witnessed a Kevin Owens face turn on the October 8th, 2018 episode of Raw after Lashley brutally attacked Owens to create an injury angle, as Owens needed surgery in real life for his knee. However, it's unknown whether WWE will go through with the babyface turn.
For all we know, they could still bring him back as a heel and have him forget about Lashley's attack. However, the best direction to go would be to have Owens and Zayn both return at the same time to target Lashley and Rush. Let's not forget that Zayn is also recovering from surgery after an injury, and his last match was against Lashley as well at Money in the Bank 2018.
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Despite the fact that there are still so many possibilities for a heel Sami Zayn, having him return by his best friend's side to take out the men that had injured both of them makes perfect sense. We've also seen Owens win all the singles titles in the WWE as a heel, so a face turn would be refreshing for his character.
Zayn has proven to be an effective face in the past, as he has been a babyface for the majority of his wrestling career. You could even have Owens and Zayn compete in the tag team division together, and they would make definitely make brilliant rivals for heel teams like Authors of Pain and The Revival.