A big part of me hopes it isn't Kane, just so that I can be surprised when the mystery attacker is revealed. Let's hypothetically say it isn't Kane... You know it's not one of the people that he's already laid out, so they would probably bring in somebody special for the event. Rey Mysterio would have the biggest reason to take out Undertaker, especially since his doing so lead to him being added into the Fatal-4-Way title match. I know it would be unthinkable to turn Rey Mysterio heel so late in his career, but honestly I think it would be awesome, and give us something we have never really seen before. If Rey Mysterio wins the World Title at Fatal-4-Way, I would be willing to bet money that he's behind the attack. Then Taker can return and confront Rey, leading to a title match.
HOWEVER, I really am convinced that Kane is the person behind these attacks. It's predictable, and Vince just loves his predictable stories. Granted, this is still really entertaining storyline, so it wouldn't be the biggest deal if Kane was the culprit. I'm thinking that Kane is revealed as the attacker, and confesses that Undertaker has always kept him in the shadows, and with him around, he was never going to get to the top where he belongs. So he put him in a vegetative state (which is so NOT PG by the way), and went on a warpath against all of the WWE. So what if we find out he's behind the attacks? His point has already been made, and he's been in the spotlight for weeks on end. Kane will become the main event player on Smackdown and he will have won either way. And then Undertaker will return and challenge Kane to one last match, because it's not big news that Kane has been thinking about hanging up the boots. If this is truly what happens, and Kane faces Undertaker one last time, I hope it's a big match, and I hope it gets the time and preparation it deserves. And for once in his entire career, can Kane please beat the Undertaker? What does Vince really have to lose by letting the Big Red Machine have his final victory? The Deadman's legacy is set in stone, no matter who he loses to at this point. Kane will face Undertaker one last time, and when he does, I truly hope he shocks the world and makes Undertaker rest....in....peace!