Do you want to know who is Kaido and his power? As of Chapter 699, hereby I conclude that Kaido is not human. Referring to “The Strongest Creature in The World”. As we can see in Punk Hazard Arc, we know that CC is producing SAD and distributing it toward Dressrosa, for DD with a SAD tanker. DD is an underling of Kaido, and its proven that DD is quite afraid of Kaido, by the effect of newspaper.
You can see in Chapter 655, the danger marks. It was seen that the Island is under marine jurisdiction, and under WG’s control. But we all can see the central mark is another thing. It could be just a simple Keep Out Danger mark for random mark made by Oda. OR it was meant for somebody. The symbol has some kind of horn, so it must be representing something with horn. Until now, there is no sign of horn boss. The Island, PH, only got dragons, random centaurs, and random half-human made by Law. How about the enemy or others?
The left characters are Monet, CC, Vergo, Yeti Cool Brothers, Brownbeard, and other weaklings.
And none of them are having any kind of horn. The only character connected with PH is DD, Baby 5, Buffalo, and Kaido. And DD has no horn, only string. Baby 5 got the weapon, no horn. Buffalo got the fan, no horn.
SO there is only Kaido.