1. Summerslam 1994 - The Undertaker vs. The Undertaker
Yes, you read that correctly and it wasn't a typo. The Undertaker actually wrestled the Undertaker in the main event of Summerslam 1994. Some backstory for you: At the Royal Rumble 1994, the Undertaker was defeated in a Casket Match by Yokozuna thanks to the interference of about ten other wrestlers. They stuffed him into the casket and were wheeling it out of the arena when suddenly a camera showing the inside of the coffin appeared on the video wall. The Undertaker delivered a soliloquy talking about ridiculous stuff until he flew through the air and "died". I know what you're thinking and no, I did not make any of that stuff up. Since it was the WWF in 1994, the plot took the stupidest twist possible as the WWF had Leslie Neilsen of Naked Gun fame looking for the Undertaker in various vignettes. To compound things, Ted DiBiase appeared on WWF television and claimed that he was bringing the Undertaker back to the World Wrestling Federation. So, DiBiase's Undertaker came out and...it was clearly not the Undertaker. It was Brian Lee doing a pretty convincing Undertaker impression but the fact that he was about 6 inches shorter than the real Undertaker made the thing pretty stupid. Paul Bearer then promised to bring the real Undertaker back to challenge this fake and the main event for Summerslam was set without the real Undertaker ever returning to television beforehand. Bearer came out with a supersized urn that somehow had a massive floodlight installed in it, thus filling the arena with light and making the whole crowd wonder what the hell they were watching. The real Undertaker made his return, wearing purple gloves and boots instead of his usual grey and they have their match. The crowd was completely silent through the entire thing, not really understanding what was going on, and the match was as terrible as two guys no-selling everything would be. They exchanged a bunch of chokeslams and Tombstones until the real Undertaker did his zombie sit-up and delivered three Tombstones to put the fake Undertaker down for good. Vince McMahon thankfully came to his senses and never, ever mentioned the fake Undertaker ever again.
