I think that there is a connection between Blackbeard and Vegapunk. Maybe Blackbeard is even a direct result of Vegapunk’s experiments.
-First clue: The drawing of Blackbeard as a child from Oda. Everybody should know about this famous drawing where Teach sits and cries.
But the most important aspect for me is the snow under his feet. The snow could mean many things. I think that the snow points to Karakuri.
Karakuri is the home island of Vegapunk and we know a lot about this place. There is always winter on this island,because so a lot of snow lies around. And through Franky, we know that Vegapunk had a laboratory on the island, also he made experiments with the animals. The drawing shows Blackbeard as a child when he lived with Vegapunk on Karakuri.
Furthermore on the drawing Teach also looked on the moon, which had a important meaning in Enel’s coverstory, too. The coverstory is about Dr Tsukimi and his little robots, who lived in Karakuri.
And I don’t want to go to deep in the details but there is a famous fantheory, which says that Vegapunk similar like Dr Tsukimi is an alien from the moon. The picture of Blackbeard and the moon could be a little clue about this theory.
-Second clue: Vegapunk studies intensively about Devil Fruits. In the story, many people give statments about Vegapunk’s genius and his successfully research about Devil Fruits.
There are also many examples of his inventions with Devil Fruits like Funkfreed.
Vegapunk created even Momonusuke’s Devil Fruit, which is an artificial Zoan Devil Fruit. You can see Vegapunk is a master of this topic with profound knowledges. And coincidentally Blackbeard exists, the only man who eats more than one Devil Fruit.
It should be impossible for a human to eat more than one. But Blackbeard did it. So my conclusion is, Blackbeard was genetically modified from Vegapunk on Karakuri. Because Vegapunk is a scientist and as a scientist you always try to make the impossible things possible and to improve human and human’s life. So Blackbeard could be Vegapunk’s attempt to improve Devil Fruits. To make it possible for humans to eat more than one Devil Fruit. Remember, Blackbeard has a unusual body, which is abnormal compared with other human beings (Marco in Marineford, Buggy in recent chapter). And maybe Vegapunk is responsible for Blackbeard’s mutation.
-Third clue: In the story so far, only two persons mentioned reading in the Devil Fruits Encyclopedia, Sanji and Blackbeard. In the backstory of Sanji you can see the book in a panel (chapter 840, page 14).
Which means Sanji as a child read this book and learned about the Suke Suke no Mi. But how was it is possible for Sanji’s family to acquire the book? Well Judge, which is the biological fahter of Sanji, worked with Vegapunk together but he had to flee. And because Vegapunk is such an expert of the Devil Fruits, he most likely owned the Devil Fruits Encyclopedia or even wrote the book himself. When also Blackbeard was a prisoner of Vegapunk, he had easy access to the Devil Fruits Encyclopedia. This would also explain ,where and how Blackbeard got all his information about the Yami Yami no Mi. Judge on the other side stole the Devil Fruits Encyclopedia on his escape. So you can explain how Blackbeard and Sanji know about the Devil Fruits Encyclopedia.
So i think it is most likely that Blackbeard had a connection with Vegapunk and maybe was even created or modified by him.
(The whole Vegapunk and Blackbeard story could even be probably a reference to the Doctor Frankenstein story)
What do you think?
*Theory by justamenwithinternet