My theory is that Blackbeard already owns a third Devil Fruit, in the form of a Mythical Octopus fruit Tako Tako No Mi, Model: Kraken or Model: Akkorokamui (Japanese Kraken). I’ve had this idea for a while, considering it as just a crazy idea, but after the revelation of Kaido’s Uo Uo no Mi, Model: Seiryu (Fish fruit), the idea of an octopus fruit is not as wild anymore.

First, I’ll go through some relevant information about octopuses, and then expand on how this relates to Blackbeard’s character.

As you all know, octopuses have a really strange body, even for invertebrates. The only animal remotely similar to them are squids. Most octopuses have 8 arms, 3 hearts and a very well developed nervous system. Actually, 2/3 of an octopus’s nervous system is located in their arms, meaning that their tentacles have, more or less, a mind of their own. If you cut a tentacle, it will continue to move, even being able to grab things, and pulling them to a now missing mouth. They can regenerate though. However, because of the arms’ high sensibility, the octopus is unable to create a mental image of its body, and has low control over its arms’ movements.

Another particularity about octopuses are their 3 hearts: though only one of these pumps blood through the whole body, the other two pump blood through each of the two gills. However, their main heart stops when they are swimming, tiring them very quick; that’s why they mostly crawl, using their tentacles. Apart from this, octopuses are known to be very intelligent, they can camouflage within their surroundings, they shoot ink. Another interesting things about them is that they rarely sleep, and even when they do, it’s in a safe space for them.

So, how does this relate to Blackbeard? Ever since his introduction in Jaya, we’ve been given hints that Blackbeard’s body is not normal, finally being confirmed by Marco at the end of Marineford. It’s possible that Blackbeard ate the Tako Tako No Mi before joining the Whitebeard Crew. While a bit of a stretch, it is not impossible for Teach to have hidden his power for 20 years.

This is also why his body is so weird. He is still a human, but because of his Devil Fruit, his body changed. Most Devil Fruit users are affected by the fruit they consume, because they modify their Lineage Factor (DNA). Luffy’s body can stretch constantly, Marco can use his flames even in human form, and Chopper retains his human intelligence no matter which form he’s in. Because his body composition is different than that of a normal person, it is possible this might be the sole reason he can sustain using more Devil Fruits at the same time. One devil fruit for each of his hearts.

However, despite giving Blackbeard a huge advantage in terms of Devil Fruit usage, his Octopus devil fruit is a burden for his physical abilities. Since his nervous system is much more spread out throughout his body, it makes him more susceptible to pain, something clearly seen every time he gets hurts. Another drawback is that his body is much more sloppy, just like an octopus, and unable to move very fast. Even his stamina is bad, as he gets tired fast and is seen to be out of breath a number of times. Remember, he is 38 pre-timeskip, and is younger than Doflamingo. Just like an octopus, he may be unable to sleep very often, and Oda may even take this a step further and make him completely unable to sleep. In the image below, you can see that, despite the punch of Luffy not dealing much damage, Blackbeard is in agony, and is even a bit tired.

Teach’s fight strategy is also very similar to that of an octopus. He relies a lot on his intelligence, avoiding combat as much as possible, and even running away when the situation is not good. He has camouflaged himself as an innocent crewmate on Whitebeard’s ship for 20 years, and even did this while being a Warlord, hiding his true intentions from everyone.

Blackbeard wearing camo pants pre timeskip, possbile reference to how octopuses camouflage. His post timeskip pants also have a similar pattern to an octopus changing colour.

There’s some other things that lead into this. The Jolly Roger of the Blackbeard Pirates features 3 skulls (reference to 3 hearts leads to what Luffy and Zoro said at Jaya) and 8 bones (tentacles). It’s also interesting how his other 2 Devil Fruits play into the theme of an octopus/Kraken. Krakens could supposedly create whirpools, and change the sea surface when they appeared (Gura Gura no Mi). The Yami Yami no Mi could clearly represent the ink an octopus produces.

In regards to the Tako Tako no Mi, Model: Kraken, like I said, the existence of a fish fruit increases the possibility of an octopus fruit being real. Octopuses can survive on land for a limited amount of time, so it would not be a problem in that sense. Regarding its special ability, specific to a Mythical Zoan, you have all the abilities of an octopus: regeneration, limbs still attacking after being cut, fitting into small places, climbing stuff with his suckers, and camouflaging, while at the same time being enormous, and using the other 2 devil fruit with its arms.