#3 Mojo Rawley
Mojo Rawley has seen his shares of ups and downs and pushes and halts during his main-roster tenure in WWE. He's been a part of a tag team, a face singles star and a heel. He won the 24/7 title but that isn't the pinnacle of success in WWE. When we last saw him, he was horsing around with Rob Gronkowski and forming a short-lived alliance with Riddick Moss.
Gronk left almost as soon as he arrived, taking Rawley back to the drawing board. Having him be a part of RETRIBUTION would give him an actual direction and others to play off of. The other members are not likely to just disappear, so this would at least give Rawley some stability. When he's been a methodical and grounded heel, he's seemed like he has had more potential to succeed. As a part of the group, he could use his physicality and anger in the faction.
Since he's had some chances, which have been taken away due to others, it wouldn't be hard to understand why he'd want to sow chaos in WWE. Rawley isn't as huge a name that would be totally shocking, like say if Roman Reigns was the leader of the group. It would still be a good henchman role for the former NFL player.