#1: The Undertaker

It still remains unclear as to what exactly The Undertaker's current status within the WWE is. The Deadman was last seen in Saudi Arabia throwing both members of Rusev Day in a casket, and it seems highly unlikely that that will be his last appearance in 2018.
Taker and Cena's match at WrestleMania 34 was one of the strangest on the card, and Taker's burial of Cena has to have some sort of long-term payoff.
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There is a lot of speculation about the two men both putting their careers on the line at next year's WrestleMania, and that does make a lot of sense. What doesn't make sense, however, is why The Undertaker would put his career on the line against a man he defeated in a matter of minutes a year prior.
The WWE will need to level the playing field if a retirement match is their aim, and having Cena pick up a victory over The Deadman at SummerSlam would be the best way to do that. Cena and Taker, despite their ages, are still legitimate draws, and an advertised match between them would no doubt help boost network subscriptions heading into the event.
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