#2 Sonya Deville
Yet another former MMA fighter on this list, Sonya Deville is one of the most interesting Superstars in WWE today. Ever since she and Mandy Rose split, the former Tough Enough competitor has been mightily impressive as a despicable heel. Her intense attitude would be welcome on RAW Underground.
Deville would have to move from SmackDown to RAW, which can be fixed easily through the booking of her rivalry with Rose. It doesn't seem like the Blue brand will offer any opportunities for her after this feud ends, so it would be best to attach a 'Loser Leaves SmackDown' stipulation to their eventual blowoff match.
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This would be in addition to the likely 'Hair vs Hair' gimmick, following the events of last week's SmackDown, which saw Deville chop off some of Rose's hair. The former is likely to lose the match anyway, making for a very intriguing future for her. RAW Underground should be part of that future.
There is something about a bald Sonya Deville beating people up on RAW Underground that feels so right. It would put her over as a major threat, while installing a nasty mean streak following a massive transformation to her look. Deville could become a vicious killer on RAW Underground, and it will be wonderful.