1.Myth: Blackbeard has a parasitic twin in his belly.
Fact: The reason Marco mentioned an “unusual body type” when speculating how Blackbeard was able to handle two Devil Fruits has yet to be explained.
2.Myth: A person can control only one Devil Fruit of each type, but are not limited to the number.
Fact: It was not clearly explained by Blueno when he said one’s body would destroy itself when one consumes two Devil Fruits. Due to the reactions of the pirates and Marines to Blackbeard’s power usage, this has been proven to be untrue.
3.Myth: Blackbeard will eventually consume a third Devil Fruit of the Zoan type since there are three types of fruits and three skulls on his flag.
Fact: While Blackbeard’s body allows him to control two Devil Fruits, the possibility of him controlling a third has yet to be confirmed since we do not even know why he can control two. It is stated that his crew is now tracking down powerful Devil Fruit users and stealing their abilities, but exactly how the stolen Devil Fruits are used is unrevealed.
4.Myth: Blackbeard has eaten the “Mythical Zoan Type: Cerberus” Devil Fruit, and because a Cerberus is a dog with three heads he’s able to consume two more Devil Fruits. The Cerberus also explains the three skulls in Blackbeard’s jolly roger, why Blackbeard carries three pistols, also how Shanks’ scar, which was given to him by Blackbeard, has three scratches on it, and why Zoro and Luffy referred to Blackbeard as “they” instead of “he” during the Jaya Arc.
Fact: First of all a fruit with such name has never been confirmed or even mentioned, second the reason Blackbeard has three skulls on his jolly roger has never been explained or given any significance, and third Oda has never confirmed any of the “evidence” given in this. Also, the fact Zoro and Luffy referred to him as “they” was that they most likely guessed Blackbeard and the other strange people they had seen were together. It is highly unlikely either Zoro or Luffy could have realized Blackbeard had such an ability, given that he shows no outward signs of any powers, like any other Devil Fruit user. And the reason of Shank’s scar having three scratches was most likely because of Blackbeard’s old weapon was similar to Kuro’s Cat Claws but only with three spike-like blades.