I think the Undertaker lost his momentum around the time he cut his hair. Eventhough I loved the Lord Of Darkness, he was one of my most favorites, I do not think it's a good idea to bring him back. The reason is simple. Everytime the WWE tries to bring back old gimmicks, they make it look ridiculous. Therefore destroying what once was so great to see. It's a shame really, but that's what they do, heh.
I still feel ashamed when I think back to Kronik and the nWo. Please don't let them destroy the Undertaker too....
