#2 Ronda Rousey

Right now, nobody knows whether Ronda Rousey will return in the Royal Rumble match. After a stunning debut year, the former UFC fighter made her last appearance for WWE in the main event of WrestleMania 35, where she was controversially pinned by Becky Lynch. Rousey could be out looking for revenge.
She is undoubtedly the wildcard of this match. There is probably a 25% chance that 'Rowdy' Ronda shows up at the Rumble but if she does, she is 100% winning the match. That is why so many people are cautious in their approach towards who could win the 30-woman match.
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The one-on-one match between Becky and Ronda might be the biggest match that WWE could book at WrestleMania and they will obviously want it to happen. The ball is probably in Ronda's court, whether she is up for the big fight. This is one situation that we cannot call, right until the Rumble.
A return for Ronda Rousey would make for another memorable Royal Rumble moment, after her debut at the end of the 2018 event.