Thanks to his training under Garp, Koby seems to have mastered all the Six Powers, which makes him quite a formidable enemy for any pirate right now.
Six Powers
2 New World he is also capable of using the Moonwalk and Tempest Kick techniques. After the timeskip, Coby has mastered his Six Power techniques. In Episode of Luffy, he shows to be able to use a technique similar to Tempest Kick, but done with his arms.
Coby has a high level of control over his Kenbunshoku Haki. He first awakened this ability during the Summit War. With the help of Kenbunshoku Haki, Coby was able to hear the voices of the people around him fading away, which implied that people were dying.
Colby has eaten the Kuro Kuro no Mi, a Logia type Devil Fruit which allows him to create, control and become shadow at will.
Koby the Hero is a Marine Captain who trained together with Helmeppo under Vice Admiral Garp's supervision.
However, Coby works under evil officials and does the bidding of the celestial dragons to a certain extent, just like all other Marines. It's no wonder that the Marines don't usually have conqueror's haki, and just like everyone else, it is highly unlikely for Coby to awaken conqueror's haki.
In a shocking turn of events, it was revealed that the Gomu Gomu no Mi is actually a Zoan type of Devil Fruit and its real name is the Hito Hito no Mi, Model: Nika. Although it may be confusing to some as to how that's possible, the basis for this was set quite early in the series.
Koby is a user of both Busoshoku and Kenbunshoku Haki, with his expertise in the latter being greater. Koby's Kenbunshoku Haki awakened during the Paramount War, and it allowed him to sense every life that was being extinguished. After the time-skip, it is very likely that Koby has refined his Haki even further.
There are rumors that Koby is going to fight against Boa Hancock, but it is very obvious that he's not ready for such a challenge. Smoker is above Koby in every aspect.
So far, the crew has been responsible for the deaths of Whitebeard, Ace, and Absalom, which shows that they wouldn't hesitate to kill Koby for their needs. However, one thing to keep in mind is that the crew only hunts devil fruit users, and Koby does not possess one. So, why did Blackbeard kidnap him?
As of where the anime currently is, Luffy can now use three of the “Six Powers” techniques.
2/10 CAN'T BEAT: Rob Lucci
Lucci is also trained in Rokushiki. Since being defeated by Luffy, Rob Lucci joined the CP-0 and improved his fighting skills. For the time being, Lucci holds the edge over Koby, but it might not last for long.
Conversation. Something interesting to note, all CP9 members are said to have observation and armament haki. Lucci was stated to have learnt it over the timeskip to get into CP0, so while they're not directly listed as such yet, this implies that all CP9 members made it into CP0!
Coby is one of the most talented characters in the series. Just two years prior, he was merely a kid with below-average strength. Now, however, he is a marine rear-admiral and a pretty strong one as that. He's strong, but not strong enough to be Luffy's match.
This is supported by the fact that Koby uses (and masters) Soru, though he has not shown the ability to use any other Rokushiki techniques.
He is a specialist of Observation Haki, Ryuo, and also Conqueror's Haki. Among all the Haki types, however, Luffy is especially skilled at using Conqueror's Haki, which is his best Haki type.
Busoshoku is perhaps Luffy's most used Haki as he commonly mixes it with his Devil Fruit abilities to increase his offensive and defensive potential.
Nami is also a competent fighter, although among the weakest in the crew. She mainly makes use of her wits in combat to get the better of her enemies. Surprisingly, One Piece 1058 showcased her using Conqueror's Haki in what appeared to be a gag scene.
We know for a fact Shanks had it and it was stolen from the world Government.
Logia. The rarest and most powerful of the three Devil Fruit types, Logia-type Devil Fruits allow their users to create, control, and transform their body into a natural element, such as smoke, sand, fire, lightning, ice, light, magma, mud, snow, plants and even darkness.
7/7 Tori Tori no Mi, Model: Phoenix
The devil fruit was eaten by Marco when he was still an apprentice on Whitebeard's ship. Like the usual Zoan-type fruits, it grants Marco extra strength and recovery in addition to his flight powers. The blue flames from the devil fruit grant Marco incredible regeneration.
Katakuri can use all three types of Haki and he can actually use the Advanced versions of both Armament and Observational Haki. Biggest Feat: Charlotte Katakuri proved to be a strong opponent for Luffy, and it took Luffy using a new form of Gear Fourth to defeat him.
Dragon is almost certainly going to be a user of Conqueror's Haki as well just like his son. In Marineford, Luffy's Conqueror's Haki was attributed to Monkey D. Dragon, meaning he is already implied to be its user despite not having used it so far. In the future, fans will certainly see him make use of this ability.
8/10 Can Become: Koby
Koby is one of the Rear Admirals of the Marines, and likely their most recent addition. He holds enough aptitude to be a member of the secret SWORD unit, which is led by X-Drake. According to Garp, Koby has a lot of potential to fulfill.