Undertaker Returning for 900th Episode of Smackdown Live

After rumors of the Phenom being done in the world of the WWE,
a light of great news showed after the WWE announced that on November 16th, The Undertaker is set to return for the 900th episode of Smackdown Live.
The last time we saw the Phenom was on April 3rd, after he defeated current Smackdown Commissioner, Shane McMahon in a Hell In A Cell Match, and has been off WWE TV since then. The question everyone wants to know is, for what?
The Undertaker has defeated many huge names in the WWE,
from Hulk Hogan, to Ric Flair, to Shawn Michaels, to Triple H,
The Phenom is unstoppable when it comes to either fighting at Wrestlemania or fighting with his career on the line.
Who could he possibly face when he makes his return? The current wrestlers on the Smackdown Live roster can go from Baron Corbin, to The Miz, to Doph Ziggler, to Dean Ambrose, etc. The WWE can build up a huge match with any of these top superstars, and all of those names could benefit from it.
But what about Wrestlemania Could this be a build up? For all we know, the WWE could be planning a match at Wrestlemania between the Undertaker and John Cena.
There are a lot of outcomes that could come. This match has been talked about for years now, and with the match possibly happening at the greatest stage ever, it is very likely to say that we will be seeing history made next year at Wrestlemania.