The Cat Claws are the main weapons of Kuro. They are a pair of furred gloves, at the end of each finger and thumb is a katana blade, which creates gigantic iron claws that, overall, resembles long cat claws. They are first seen vaguely being used against Merry, and then properly seen and introduced against the Nyaban Brothers.
As a reference to remembering how to kill, Kuro pushes his glasses up with his palm, in order not to scratch his face with his claws.
Kuro primarily uses these giant claws in conjuncture with his superhuman speed to strike his opponents with such swiftness that they will not know what struck them until it is too late. Using this as a base of his special technique, Shakushi, he runs around at uncontrollable speed, killing anything his claws connect with at random, including his own crew. Oda confirmed Kuro's Shakushi and CP9's "Soru" ability travel at roughly the same speed. The difference is when Kuro uses that technique, he cannot tell what he is attacking, whereas CP9 have mastered this ability and therefore can, a difference that renders Kuro vastly inferior to the CP9.
Nuki Ashi (抜き足,Nuki Ashi?, literally meaning "Stealth Foot"): An ability in which Kuro moves to a certain location (usually behind an opponent) very quickly, moving about 100 meters in 4 to 5 seconds, almost looking like he teleported. He initiates this move by performing several quick foot movements to propel himself to another location, much like CP9's Soru, except that the movements of his feet are more noticeable, suggesting that this ability is a rudimentary form of Soru. This technique is called Pussyfoot Maneuver in the Viz Manga and FUNimation dub and Stealth Walk in the 4Kids dub.
Creeping Cat: Like the Nuki Ashi, except he has more control and moves about freely while appearing invisible. The downside is, he needs to revert to normal speed when initiating attacks, making him automatically visible at that point. The same thing also happens if, by any chance, the opponent(s) should manage to strike out at him while he's in this state. This is a technique name that comes from the English versions, as this is simply another use of the Stealth Foot in the Japanese version of the series. This move is one of his super attacks in the One Piece Grand Adventure
Shakushi (杓死,Shakushi?, literally meaning "Death Scoop"): Kuro's ultimate technique. A fearsome attack that allows him to sweep a large area, killing anything his claws connect with at random, including his own crew. The order in which he inflicts his attacks are so random that they range from mediocre scratches to fatal evisceration to both friend and foe alike. He moves so fast even he does not know what he's attacking, and only stops when tired out (or when someone can catch and physically stop him, as Luffy did). He initiates this move by swaying back and forth sideways in a fluid manner — this is necessary in order to enter the "trance" needed to perform the move. In the anime this move has the side-effect of generating purple clouds of smoke to rise from the ground as Kuro moves at his topmost speed. It is said that he killed many of his own crewmates in the past with this technique. In Unlimited Cruise, Kuro seemed to have refined this attack, by focusing onto his opponent with multiple strikes, rather than a widespread carnage.
The name of this attack comes from the Japanese phrase "neko mo shakushi mo" (猫もしゃくしも,neko mo shakushi mo?, literally meaning "even cats and rice ladles"), which is a Japanese figure of speech, meant to mean "absolutely everything", reflected in the fact that this attack indeed attacks "absolutely everything". The word "Shakushi" is homonym with "Rice Ladle". It's also a pun of the Japanese word, Sakushi which means schemer, hence Kuro's personality.
This is called Out of the Bag Attack in the Viz Manga and 4Kids and FUNimation dub, this translation appears to be in reference to the phrase "Cats out of the bag", this is also coincidental to the fact that he uses it after his secret is "out of the bag" and he uses it in an attempt to kill everyone in the area who knows his secret.