Kaido (カイドウ) has such incredible strength. But, to be one of the Yonko, it takes strength beyond even an Admiral level and there must be an explanation for Kaido. The most normal person I've known as Yonko is Shanks, but since he possesses incredible and powerfull Haki so it makes sense. But Kaido? Does he have mysterious power other than just being physically strong?
From One Piece Wikia :
Perhaps the greatest sign of Kaido's strength is his apparent inability to die. He has been caught and tortured 18 times, and people as powerful as the Marines and other Yonko have attempted to execute him 40 times. However, he mysteriously survived every single attempt because every single execution weapon broke when being used on him. Most notably, Kaido has jumped from 10,000 meters in the sky onto the ground, creating a massive shockwave strong enough to sink a large ship nearby, and emerged without an injury; it has even become a hobby for him to attempt suicide, only for it to fail.
That's not enough explaination about Kaido's power.
Here is the thing, you know Admiral Akainu (赤犬), possesses the Magu Magu no Mi which grants him the ability to transform his body into terrifying magma and manipulate it at will, he can even afford to crush a land if he wants. But hey, that's not enough to match a Yonko.
So back again to Kaido, Does he have any other mysterious power?