#4 Vulnerability
Moving away from The Deadman persona adds a completely different dimension to The Undertaker character. Gone is the air of invincibility of The Undertaker that is associated with The Deadman.
The Biker gimmick allows Taker to become a lot more vulnerable in his remaining feuds with WWE. The Deadman version, it is a lot more difficult to do "jobs" and "put guys over". The Undertaker has built up such a mystique and legend over the years as The Deadman that only the cream of the crop should be able to pin or submit The Deadman.
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Whereas, The Biker version is more human. The Undertaker becomes a lot more vulnerable to defeat. At this stage in his career, The Phenom is certainly more focused on helping WWE Superstars "get the rub" and make it to the next level in WWE by working with The Undertaker and eventually defeating the future Hall Of Famer. The Biker version of the character, The Undertaker can easily be defeated by WWE Superstars without it hurting the mystique and legend of The Deadman.