Since he’s accomplished so much in his WWE career, U.S. Champion John Cena may make it a little too easy to forget there are still challenges lying before him.

Those elusive goals unexpectedly grew by one at WWE Elimination Chamber 2015. Because he simply didn’t get the job done against NXT Champion Kevin Owens, the Cenation leader now must answer to critics who debate whether “his time is up,” a topic that Cena probably didn’t plan to ponder when he arrived in Corpus Christi, Texas, on the final Sunday of May. As a result, Cena’s more immediate “to do” list includes one new objective: teach the NXT upstart a lesson at WWE Money in the Bank 2015 by any means necessary.

Watch Elimination Chamber 2015 on WWE Network |  Cena vs. Owens match photos

Still, Cena’s misstep with Owens left the WWE Universe asking: What other exploits yet linger on the four-time U.S. Title holder’s WWE bucket list? From a championship that’s missing in his trophy case to a Phenom-enal WrestleMania run he’s trying to catch, take a look at five accomplishments that John Cena has yet to achieve in WWE.

Experience an Intercontinental Title reign

At WWE Elimination Chamber 2015, Ryback left his first Chamber Match victorious despite facing five Superstars with substantial experience within the unforgiving steel structure. His prize? The vacant Intercontinental Championship, which officially placed the beastly brawler in an exclusive club of WWE Legends including Pat Patterson, Bret “Hit Man” Hart and Chris Jericho.

Surprisingly, that’s also a club that excludes the Cenation leader.

Review Ryback's place in the Hall of Intercontinental Champions

John Cena is no stranger to squabbles with reigning Intercontinental Champions, having crossed the paths of Rob Van Dam, Umaga and Dolph Ziggler, among others during their respective reigns with the coveted title. However, the reigning U.S. Champion just never found himself in position to officially challenge for one of the most storied prizes in sports-entertainment. That said, Cena’s talent and arsenal make him an immediate threat if he ever chooses to chase the Intercontinental Title, even against a sizable champion like the man they call Ryback.

Rule as WWE King of the Ring

Only 19 Superstars to date experienced an official coronation as a WWE King of the Ring. Seven of them eventually earned their place in the WWE Hall of Fame, with that number likely to grow in the coming years. And all of them did it by winning the only tournament in sports-entertainment in which victory can truly be described as a crowning achievement.

Watch the 2015 King of the Ring Tournament on WWE Network

The biggest hurdle keeping Cena from realizing this dream may be the march of time. The WWE King of the Ring Tournament doesn’t occur with an open challenge, and it does involve going through multiple opponents in one night. Cena witnessed this recently when King Barrett achieved the feat in April 2015, but will need to bide his time and remain ready to compete when the next edition of the elusive tourney occurs.

Outlast The Undertaker in consecutive WrestleMania matches

Though his vaunted 21-match undefeated Streak at WrestleMania is over, The Undertaker still holds an active record that few, if any, Superstars could ever dream of matching. That’s because The Deadman presently owns the active mark for the most consecutive matches on The Grandest Stage of Them All, a run he extended to 15 bouts in a row when he defeated Bray Wyatt at WrestleMania 31.

See The Undertaker's dramatic WrestleMania 31 entrance on WWE Network

So, who’s the closest to catching The Undertaker? John Cena, whose victory over Rusev at Levi's® Stadium in March 2015 extended his active streak of WrestleMania matches to 12 and counting. Cena’s dozen contests at The Showcase of the Immortals tied him with two Superstars for second place on the list: Bret Hart, who didn’t miss a WrestleMania between 1986 and 1997, and Randy Orton, who, like Cena, is riding an active 12-match streak of his own.

Defeat Mr. McMahon via pinfall

It takes a great deal of effort to draw the ire of Mr. McMahon, and even more so to anger the WWE Chairman to the extent that he decides to compete inside the squared circle. John Cena just happens to be one of the Superstars to accomplish that feat, but the results from his two encounters are best described as … mixed.

WWE Network: Find out who Mr. McMahon faced in his first WWE match

To date, the Cenation leader cannot exactly point to a defining victory against the McMahon Family patriarch. In 2006, Cena defeated Mr. McMahon on Raw via disqualification — a result that likely didn’t feel like a win, given he was rewarded with a sledgehammer attack by Triple H. Four years later, the WWE Chairman pinned Cena on Raw after McMahon amended the match stipulation from a one-on-one encounter into a Handicap Gauntlet Match in his favor.

That puts John Cena in the company of "Stone Cold" Steve Austin, Brock Lesnar, Randy Orton and other opponents who had "no chance in Hell" of keeping the CEO’s shoulders down for a three-count. Should a rubber match between two of the most influential forces in sports-entertainment ever materials, the WWE Universe should know better than to think Cena might give up on achieving the elusive goal of pinning Mr. McMahon.

Match Ric Flair’s 16 World Title wins

To be the man, you’ve got to beat the man. And if John Cena wants to be “the man” in WWE lore, he’ll need to exceed the most celebrated accomplishment of the “Nature Boy.”

If he can become WWE World Heavyweight Champion just one more time before he hangs up his wrestling boots (or sneakers), the Cenation leader will tie Ric Flair’s 16 World Championship wins, a feat once thought impossible to match. And if Cena can claim one more title reign after that, the World Title record will be his alone.

Relive Ric Flair's last WrestleMania match on WWE Network

While Cena still has time to realize this once-thought-unimaginable feat, this is still the WWE World Heavyweight Championship we’re talking about here. One doesn’t just fall into those title reigns; instead, a challenger scratches and claws his way into the opportunity and, if he’s at peak fitness and fully prepared, maybe, just maybe, he endures to become the new champion.

The WWE Universe knows that Cena has the fighting spirit to match Flair’s mark, but the question is: Will he be ready when opportunity knocks?