User blog comment:Yatanogarasu/What Did Blackbeard Do to Get the Gura Gura no Mi?/@comment-3242083-20101231211628

I think it is a mix between your option 2 and 3. The Yami Yami no Mi is able to extract another devil fruit power, but only when the users body is dead/disabled. Maybe he can "intercept" the abilities while the fruit leaves its old masters body, before it can re-grow somewhere else. Probably the reason why he wanted/needed Whitebeard dead. I don't believe he can handle 2 fruits because of the yami yami no mi, but as your third option states: he is just a freak of nature, like so many characters in one piece. He is simply durable.

For option one, i don't believe Vegapunk was able to extract Kizarus "power". I believe Kizaru just played a vital role in the development of laser technology. More like an example of how lightbeams form and how they become destructive. Imagine Enel would have lived in the real world, around 1800. The invention of electricity would have been a piece of cake with a person that is able to produce and become electricity. Something real to study.