While this may never be possible now that the Undertaker has retired, these are some of my biggest fantasy matches in which if i were a booker - i would plan them immediately. It's unfortunate that WWE could not plan these official matches. I thought some of the Undertaker's matches were unnecessary like a second Kane match or a second Triple H. If the Undertaker still had his undefeated streak, this is how i would've written his legendary match cards.
The Undertaker vs. Kurt Angle - If i were a storyline writer, i'd have Kurt Angle taunt the Undertaker, flaunt his win at No Way Out, put him through the ankle lock again, then finally take his Athleticism to the next level - end the Undertaker's undefeated streak. Both are very competitive fighters as Kurt Angle has experience in legit amateur wrestling while the Undertaker is experienced in MMA. Both have devastating submission holds but which one would dominate the ring - the Ankle Lock or Hell's Gate?
The Undertaker vs. John Cena - Both have legendary careers. John Cena has had more titles than the Undertaker and equally devastating moves. John Cena has enormous strength and great story-telling abilities. He's been in several main events like the Undertaker has. They only wrestled a couple of times ending usually in a no-contest. I would've written an ambitious rivalry between the two for a shot for a WWE title at Wrestlemania. Perhaps making an "I quit" match would be more suitable.
The Undertaker vs. Stone Cold - This would've made a huge main event during the Attitude Era since Stone Cold and Vince McMahon were feuding at the time. If Vince unfairly booked Stone Cold to face the Undertaker in a streak vs. career match, it would've gained so much potential. Both are brutal in their approaches to wrestling in the ring. Stone Cold is a brutal legendary brawler when it comes to a detested opponent. He would be the ideal candidate for the Undertaker seeing how their championship matches went.
The Undertaker vs. Goldberg - From the matches i've seen from Goldberg, he's a devastating wrestler in the ring. His finisher is ridiculously painful from the looks of it. Goldberg is a dominant athlete and an aggressor. Goldberg is very strategic in his approach like the Undertaker.
The Undertaker vs. Sting - Rather than feud with the Authority, i'd have Sting feud with the Undertaker for a match at Wrestlemania. To make things more interesting, i'd book it at Hell in a Cell match. Both are similar in stature, signature moves, submission holds, appearance, and legacies. After all, both men probably wanted to have a match together before Wrestlemania 32.
I'll reiterate, t's a shame that these matches never occurred for whatever reason. Nevertheless it's nice to dream about what could've been differently.