It's important to note that Yamato and Kaidō's horns are, in fact, parts of their bodies. A possible explanation would be that the two simply wear headpieces that look like horns, which means they're still, technically, ordinary humans.
The Oni are a rather mysterious race as almost nothing is known about them. They haven't been officially introduced in the series yet, but there is no doubt that they will be confirmed as a separate race, sooner rather than later. There are two known members of this race- Kaido and Yamato.
Not only did they get to see Kaido's long awaited flashback, they also saw Luffy deliver his finishing blow. The Straw Hat even managed to break the dragon's horn in the process, sending him straight into the ground. Speaking of which, many readers have given props to Kaido himself.
Flame Dragon Torch is, without a doubt, Kaido at his very strongest. Not even someone as strong as a Yonko can get near him in this state, as seen when Luffy has to let go of him due to extreme temperatures.
The Dragon Horn is a small black horn that enables the one who blows it to summon and control a dragon. It first appeared in the one-shot manga Monsters.
After his death, Yamato chose to become just like Oden, impersonating him and adopting his mannerisms. As a result of this desire to emulate Oden, Yamato decided to become a man and identify as Kaidou's son, and Kaidou and his crew refer to him as such as well.
Luffy ended up meeting ol' Red-Hair when he was a young boy. Shanks took a liking to the child, and gave him the straw hat off his head as a gift. Luffy promised to return it to Shanks when he became The Pirate King.
Although he did fight Kaido and even managed to earn his praise, which is quite impressive, it was pretty clear that Zoro wasn't anywhere close to him in terms of either power or skill. That in itself is a big reason why Zoro would never have killed Kaido. For now, Zoro is levels below his Captain, Monkey D.
Oden was a very strong character, and he was able to fight against the likes of Whitebeard and Roger. Oden faced Kaido in Wano and gave him a huge scar. Oden's swordsmanship combined with his Haki was enough to bring down Kaido to his knees.
Kaido is the strongest living creature in One Piece. As such, he presents a threat few are able to counter. His scales, in particular, are nearly indestructible, only being cut by legendary swordsmen like Oden and Zoro. However, Kaido's defenses belie a serious weakness to advanced Armament Haki.
When the Scabbards were on their way to Onigashima to confront Kaido, Kanjuro revealed himself to them in a dramatic manner. He admitted that he did not mean any harm but wanted to act out his role. While revealing himself as the traitor, Kanjuro was unapologetic and happy to see the baffled looks on their faces.
1 Has Defeated: Kozuki Oden
Oden engaged Kaido in a massive battle at Wano Country's Udon region 20 years ago. Although Oden lost the battle, in essence, he defeated Kaido.
King the Conflagration is one of the three All-Stars of the Beasts Pirates and Kaidou's right-hand man. Born as Alber, he is a member of the near-extinct lunarian race from the Red Line, noted for their ability to create fire.
Garp Is Considered To Be One Of The Strongest Marines. Also renowned as 'Garp The Hero' and 'Garp The Fist', Monkey D. Garp is a Vice-Admiral of the Marines. Being their strongest known member in history, there's no denying that Garp is capable of taking on Kaido.
Concerning his ethnic appearance, Oda revealed that he imagines Zoro to be of Japanese descent, albeit in a real-world context.
Black Maria is a youthful woman of incredible size by human standards. She is 8.2 meters tall, being slightly larger than Kaidou himself. Her long blonde hair is styled like a geisha's, with two swords notably being part of its arrangement.
Yamato was capable of holding back Kaido and that's all an Admiral has to do. Kid and Law took down Linlin, two Admirals would decimate her. Once that happens, Three Admirals at the same time vs Kaido would destroy him in a minute.
Despite being a Vice-Admiral, his strength surpassed that of an Admiral. Garp has previously fought characters such as Roger and Whitebeard and is spoken about in the same breath as them. Someone like him is bound to be stronger than Dragon, at least in his prime.
Immediately after, fans saw Law and Kid team up against Big Mom and take her down. This was soon followed by Luffy awakening his Devil Fruit and taking Kaido down as well.
One Piece 1049: Luffy Triumphs Over Kaido.
Kozuki Oden and Roronoa Zoro both gave him permanent scars with their swords attacks. Keep in mind that neighter fighters have unlocked the ability to forge "black blades." Mihawk should be strong enough to scar Kaido as well. It should also be noted that Kaido considers Shanks to be his equal.
Shanks' scar caused by Blackbeard because he's mistaking the gomu no mi with yami no mi which Blackbeard been searching for decades. We know how willpower work on One Piece, man dreams never die.
In addition, Nico Robin and Sweet Pea have also worn Luffy's straw hat without his permission.
We know that the current owner of the Straw hat is no other than the Straw Hat Pirate's Captain, Monkey D. Luffy. We learnt how he got it and who gave it to him, which is the Captain of the Red Hair Pirates, Shanks.