After several names were tossed around, the plan for months was John Cena vs. Undertaker at WrestleMania 34.
Before their match, Elias tried to perform a song before being taken out by Cena. As Cena exited up the ramp, Undertaker appeared and won a squash match in minutes.
After WWE decided to move forward with the match, they realized Undertaker was unable to do much in the ring. So, WWE never confirmed the match as there was never a guarantee Undertaker vs. Cena would happen.
WWE wanted fans to watch the show with the idea that Undertaker would appear, but decided to not make it one of the marquee matches.