Can't forget Undertaker vs Undertaker and Kane vs Kane.
Undertaker battling a doppelganger of himself actually headlined a Summerslam (if you can believe that, and over a very excellent bout between Bret Hart and Owen Hart inside a steel cage, too), and the Kane vs Kane stuff was even worst once you know the intention behind it. Glen Jacobs was giving serious thoughts about retiring around this time (this was 2006-ish), but they loved the Kane character so much that they wanted to keep him around, so their intention was to pass the character on to someone new by revealing that the 'new' Kane had actually been the real one all along (brother of the Undertaker, physically/mentally scarred by fire, etc.) and that the Kane we were all familiar with (as played by Glen Jacobs) had actually been an impostor for all these years. However, Kane decided not to retire and so the angle was put to rest.
