
Originally Posted by
onepiece.wikia.com
At some point in his life, Teach once fought Red-Haired Shanks and caused him the scars on his left eye, noteworthy as he had not eaten his Devil Fruit yet and Shanks claimed the fight was not a sneak attack. Having wounded a member of the Yonkou, without gaining any Devil Fruit abilities prior to that point speaks volumes of just how powerful Blackbeard is. In fact, after the Battle of Marineford, Blackbeard has proved himself to the Gorousei that he has a one-step lead to the empty position of Yonkou that Whitebeard once sat on.
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Another indication of his strength is stated in the conversation between Shanks and Newgate. Shanks claimed that Blackbeard did not want to make himself known to the world yet, which is why he didn't become a commander. With that said, his strength is easily on par with any of the other commanders.
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Teach has more than proven that he is one of the strongest characters in the entire One Piece series, possessing the extremely powerful and dangerous Yami Yami no Mi and Gura Gura no Mi Devil Fruits, as well as his immense physical strength and endurance. He was able to bring Luffy and Ace to the point of defeat in just one single punch. Now that he posseses Gura Gura no Mi's quake charging powers, it is possible that his punches are even stronger and lethal.