Vegapunk confirmed why Blackbeard can have multiple Devil Fruits
Through an unknown method, Blackbeard became the first and so far, only known person to wield the powers of two Devil Fruits at the same time. Marco speculated that this was possible due to an unstated peculiarity unique to Teach himself, having to do with an “atypical body structure” of some sort. He also pointed out that the other Whitebeard Pirates should be aware of this fact.
With the power of darkness (the Yami Yami no Mi), which “reduces anything to nothingness”, and the power of earthquakes (the Gura Gura no Mi), which “brings destruction to everything”, Teach claimed himself to be truly invincible and the strongest of them all.
Teach has since attempted to acquire other additional Devil Fruits such as Boa Hancock’s Mero Mero no Mi and later Trafalgar D. Water Law‘s Ope Ope no Mi, though it is not known if he has acquired any more abilities yet or how many he has in total.
It’s been long theorised that Blackbeard’s ability to eat multiple devil fruits comes from a kind of split personality he has. Has Chapter 1103 confirmed this?
This panel is why I say this.
What if the Marines did get some of Blackbeards blood/DNA when he became a Shichibukai and when Vegapunk tested it he got the idea for his “switch” that is like a “split personality” from that?
His ability that gives him the split personality to allow him to never sleep and eat multiple devil fruits and could have shown up in his blood and Vegapunk thought he could use that to create said switch.
The timeline fits. If this panel is just before the Marineford war, it would be right after Blackbeard became a Warlord. Enough time for Vegapunk to think up this idea but not test it.
*Theory by Certain_Guitar6109