There has been much debate as to who should and will face the Phenom at "the grand daddy of them all," Wrestlemania 25. Here is a list of potential candidates for this position, and the probability of the matches actually occurring.
Umaga - The return of Umaga to SmackDown! is imminent, and many believe that this return will occur at the Royal Rumble. What better way for Umaga to make his impact felt than by taking out the Undertaker in the Rumble match? This feud was expected to take place when Umaga was drafted to SmackDown!, but injuries forced Undertaker to feud with the Big Show. Umaga has had some pretty decent matches with wrestlers that can lift him (i.e. John Cena) and the Undertaker would be more than capable to perform the feat. However, Umaga seems destined for a major push, and since he would not be able to do this on either RAW or SmackDown!, he is most likely headed to ECW. There is still the possibility of these two feuding in the future, but probably after WM 25.
Probability = 25%
Vladimir Kozlov—The Russian mauler has been on a course of destruction ever since he debuted on SmackDown!. He has never been pinned before by any WWE Superstar. He can put this streak on the line against the best streak in all of sports entertainment. Undertaker has been in many feuds where he was equalled in strength, and this would be no different. The problem is that Koslov has been given main event spotlights at PPVs before, and his lackluster performances have really pushed him down the totem pole. I have a feeling that he will be in a match with either the Big Show or the Great Khali (maybe even both).
Probability - 35%
Triple H—These two competitors have had some great feuds in the past, including a WM 17 bout right in the Undertaker's own backyard: Houston, Tex. Eight years later, the two could be destined to meet once again in the same stadium. It would no doubt be a great matchup between the two, and the fans would really be into it. The reason why these two will not meet one another this year is simply because a match between them would have to be for the title. With both being baby faces on SmackDown!, it really makes no sense to pit these two together, unless HHH turns heel. This probably will not happen, as I fully expect him to win the Elimination Chamber at NWO, and then face Edge for the title.
Probability = 55%
Shawn Micheals—Rumours have been circulating for months that Micheals approached the writers and asked for a bout at WM 25 against the Undertaker. This dream match would pit Mr. Wrestlemania against the man who has dominated Wrestlemania. The two would put on a show in front of their home state crowd, and many would probably say this match would go down in history. However, with the interesting angle between JBL and Micheals, it seems highly improbable that Shawn would get out of this feud and begin one with the undertaker in less than two months. That being said, WWE could still put this match together in time for WM 25.
Probability = 60%
Chris Jericho—My personal pick for the Undertaker's opponent at WM 25 is none other than Chris Jericho. Jericho has essentially feuded with all of the top faces on RAW and has been embarrassed the past few weeks by the McMahons. With Jericho in the Royal Rumble match, I can see the Undertaker eliminating Jericho, and then Y2J returning the favor later on in the match. Then Jericho can jump over to SmackDown! to continue this feud with the Undertaker that could result in a match at WM 25. This match could live up to the potential of one of the greatest Wrestlemania matches of all time. This feud can also go past WM 25, just like the Edge-'Taker feud from the past year.
Probability = 85%
Wild Card Pick : John Cena—If you were to ask any WWE fan to pick a dream matchup they would like to see at WM between any two current Superstars, they would more than likely choose Cena and 'Taker. Now most people would consider this a pipe dream, but let me try to explain how this match could possibly come about:
First, the Undertaker would have to win the Royal Rumble match, and Cena would have to win his match. But for Batista's injury, he would have been Cena's opponent at WM 25. The Jericho-Cena feud has already been done. It would have been more than likely that Cena would face Orton at WM 25, but with this Orton-McMahon angle now popping up, Stone Cold Steve Austin may make his return for one last match against the Legend Killer. So where does that leave Cena? Well, the Phenom would have his choice of either Cena, Edge (see my RR predictions), or Jack Swagger. He has already gone through a long feud with Edge, and Swagger is still too young to be in a feud of this magnitude. That leaves Cena and 'Taker, which would be a dream come true for all.