Law is shown to have a very strong will as he, along with most of his crew, proved resistant to Rayleigh's burst of Haoshoku Haki that took out almost everyone in the Auction House. This feat caused Rayleigh to comment on him being a fearsome pirate. He was also able to withstand the clash of Haoshoku Haki between Luffy and Doflamingo.
Even Donquixote Doflamingo commented to his subordinates at Punk Hazard about Law's potential while comparing it to Luffy's, which Doflamingo witnessed himself during the war at Marineford two years ago. Doflamingo saw talent in Law and intended to make him into his right hand man. He reserved the Heart seat for Law, showing that the latter is considered on the same level as the elite officers of the Donquixote Family. Vergo was only able to keep ahead of Law because he had the latter's heart at the time, a situation that immediately reversed after Smoker (reluctantly) helped Law to retrieve the organ.
He is also apparently quite fearless, as he allowed several Marines to get within close-range of him on Sabaody Archipelago, despite being a long-range fighter. During their stay at Sabaody Archipelago, the Kid Pirates and Heart Pirates were caught in a battle with a Pacifista. The end of the battle was unseen, but since they reappear during the Marineford Arc, it can be assumed that they either defeated the Pacifista or managed to elude it. Kizaru mentioned that the Heart Pirates did a good job at running away.
Sometime during the timeskip, Law has become so powerful and infamous that even the ruthless Marines of G-5 were deeply afraid of him. He had gained a bounty that surpassed Luffy's at the time, and brought a hundred pirates' hearts to the World Government, earning him a position in the Seven Warlords of the Sea. Law was able to battle and eventually defeat Smoker, a Marine vice admiral and a Logia user without getting himself seriously injured. He also defeated Vergo in one move while before, in the past, he was unable to even harm him. He is now strong enough to counter attacks from an Admiral and a fellow Warlord at the same time, like in his confrontation with Issho and Doflamingo. During his time in Wano, he is able to hurt both Kaido and Big Mom, both Emperors who are known for their incredible durability.
In addition to his Devil Fruit, Law underwent an extremely rigorous combat training regimen under the Donquixote Pirates as a child, attaining incredible superhuman physical prowess. While still a twelve year old boy, he was already strong enough to throw Rosinante, a very tall and large man, by grabbing him by the leg. Additionally, he has the physical power to block Doflamingo's extremely powerful Overheat string which shook the Thousand Sunny with just his sword. He easily wielded Kikoku, a sword as tall as himself with great speed, and is able to slice enemies faster than they can react as well as keep up with Doflamingo.
He has also displayed exceptionally great endurance, as he had his heart directly crushed to the point where he lost consciousness, only to recover shortly afterwards. In addition, he was also capable of enduring a prolonged brutal beating from Vergo which resulted in him becoming severely bloody before defeating him in a single blow once Smoker had retrieved his heart. Even as a child dying from from the incurable Amber Lead Syndrome, Law was able to keep up with the very harsh training regimen of the Donquixote Pirates of which even adults could not keep up with. Even when his disease reached a fatal stage, he could survive two ruthless beatings from Vergo. During the Worst Generation's fight against Kaido, law took a Thunder Bugua from the Emperor, and managed to not only stay conscious, but also retain enough energy to go and challenge Big Mom, something Luffy couldn't do.
Even when he was defeated and injured by Donquixote Doflamingo and Admiral Fujitora, as well as pinned to the ground by Issho's Devil Fruit power, Law was able to quickly recover and escape.
During his second confrontation with Doflamingo, Law was able to fight him and, even though he was still wounded from their first encounter as well as having his right arm severed while being brutally assaulted further, he was able to continue fighting and deal Doflamingo a severe wound with his Gamma Knife move. Also, even though Law was incapacitated by Trebol, he was still able to use his Devil Fruit Power to control his severed arm as well as defeat the officer.
Law also has formidable skills in martial arts, having been trained in this aspect by Lao G. In the anime, Law was able to hold his own against Luffy, an extremely powerful fighter in a fist fight, when Breed forced Luffy to fight Law through the Peto Peto no Mi. With Busoshoku Haki, Law could block against Doflamingo's Goshikito with his arms crossed in a defensive stance. Even at age 13, Law could defeat both Penguin and Shachi, who were bullying Bepo, a mink who is a natural born fighter, impressing them to the point they swore loyalty to him.
Since childhood, Law was already well versed in medicine, having attended an academy for medical science, while his father, the best doctor of Flevance, personally taught him the more intricate procedures. Even after he joined the Donquixote Pirates, he still retained a profound understanding of medical science, as he was able to use the Ope Ope no Mi to remove all traces of the Amber Lead inside his dying body. This was noteworthy as he was able to find a cure for the poisoning that was said to be incurable and live past the age he was supposed to die at. His medical aptitude was what led Donquixote Rosinante to conclude that Law was most compatible with the fruit, which prompted him to secure the Ope Ope for Law after he received information from both his brother and Sengoku of the fruit's present whereabouts at the time.
He earned the nickname "Surgeon of Death" due to his immense surgical skills in addition to his formidable combat abilities. He was able to simultaneously operate on both Luffy and Jinbe right after both of them barely escaped a murderous Akainu who inflicted brutal life threatening injuries that left them on the brink of death and was successful in treating them. The mere fact that he was able to stabilize Jinbe's condition strongly hints that Law's medical expertise is not limited to human anatomy alone (though human and fish-men share the same blood, so it is possible that they have similar anatomies). He later volunteers to find a cure for the children's condition at Punk Hazard, showing that he is also very knowledgeable in pharmacology. The fact he was able to apply pharmacology knowledge into his Devil Fruit powers so as to remove most of Caesar's deadly NHC10 drug out of the children's bodies, though not completely, is a noteworthy feat and is something even Chopper was amazed by.
The spatial powers given to him by the Ope Ope no Mi allow Law to perform even the most complicated and difficult surgeries perfectly with great ease, as they allow him to cut a patient's body open and remove organs without damaging any tissues, leaving scars, or causing the patient to bleed a single drop of blood while removing any disease-causing impurities as well as poisonous substances and narcotic drugs from the patient's body. This was demonstrated, off screen, during the conclusion of the Punk Hazard arc, in which he had treated the children with a series of surgeries that involved cutting the children's bodies apart in a manner that initially made Chopper believe he had killed them.
As a boy, Law was able to remove all the poisonous amber lead inside his dying body thus curing himself of the Amber Lead Syndrome while proving his capability to use the Ope Ope no Mi for treating even incurable diseases. Law could also apply his medical knowledge of anatomy into his Devil Fruit powers for combat, such as aiming his Sterben technique directly at Trebol's real body which kept hidden under a large amount of mucus disguised as a large body or precisely removing important and delicate organs of powerful enemies such as the heart which would render them vulnerable to lethal harm such as death, which was proven when Law extracted Monet's heart with his power and gave it to Caesar, who fatally stabbed Monet's heart while bypassing her defensive powers as a Logia user, effectively killing her, Law, as well as Sanji and Bege, was able to keep Caesar who is also a Logia user and a dangerous criminal under complete control due to having taken his heart hostage which was removed in a similar fashion, and the fact he used his anatomical knowledge to invent the Gamma Knife technique on his Devil Fruit which could fatally rupture and destroy the internal organs of even a Warlord of the Sea like Doflamingo further proving the fearsome way Law could actually weaponize his medical knowledge. Likewise, he also managed to pinpoint Kaido's heart in his Dragon form to caused him significant damage with his Gama Knife.
Law is a very crafty and opportunistic leader and also a highly skilled strategist, being the only member of the Worst Generation to voluntarily rest in the Paradise half of the Grand Line for at least two months before entering the treacherous region of the New World, proving great caution and tactical preparedness. He obtained the title of Warlord of the Sea in order to avoid detection of his actions and easily sail through the New World. While in Punk Hazard, Law secretly swapped numerous Seastone chains with ordinary chains as a future precaution that proved to be critical in allowing him to stealthily escape from Caesar's cage that is about to be exposed to the deadly Shinokuni gas.
As Vergo noted, Law concocted a multi-layered plan to cripple Doflamingo's Smile trade by destroying the SAD production facilities on Punk Hazard as well as abducting Caesar, the only person who knows how to create the unique substances. Through this plan, Law managed to force Doflamingo, an extremely cunning and resourceful pirate in his own right into a utterly disadvantageous choice of quitting the Seven Warlords of the Sea and facing the Admirals or keeping his position and face Kaido's wrath. He was able to fool Doflamingo into believing he killed him by swapping places with a foot soldier when the latter shot him repeatedly and retaliated when the latter's guard was down. When badly weakened, Law resort to tactically defeat Trebol, tricking the latter into letting his guard down to finish him off with his Sterben technique.
When Kinemon's original plan had been exposed by Kanjuro, Law was able to instantly formulate a backup plan, taking advantage of Luffy and Kid's headstrong and reckless nature to create an effective diversion while using it as an opportunity to transport the Nine Red Scabbards to Kaido's residence by sea using the Polar Tang and his Devil Fruit powers.
Law ate the Ope Ope no Mi, a Paramecia-type Devil Fruit which allows him to create a sphere of light blue aura, inside which he can manipulate the fabric of space. He can manifest this aura sphere over a very wide area, however he cannot move the sphere once he’s conjured it, he would instead have to dismiss the sphere and create a new one in a different location. Furthermore, Law has to concentrate in order to maintain and use his power, and unlike most Devil Fruit powers, Law's powers directly take a toll on his stamina.
Inside the aura sphere, he can exert complete control over the fabric of space, referred to as the ability to "operate" on anything within the spherical "operating room"; he can move things within the area of the sphere telekinetically and make things, including himself and other people, swap locations via teleportation. However, he cannot move other people with strong Haki very far, as they possess more resistance to Law's power. He can also swap incorporeal things, such as souls, resulting in the victims swapping bodies. He is also able to cut things from a distance and without actually damaging them, as well as reassemble things into various combinations; he can even attach living body parts to inanimate objects. Living things cut into pieces by this power remain alive and still able to move, even if the head is removed from the body.
This power can also be used for medical purposes; Law can completely remove harmful matter, such as drugs and diseases, from organic tissue. Additionally, he can attach new body parts to a persons body to replace destroyed body parts. He can also use his power to scan anyone within the sphere in a manner similar to an X-Ray machine.
Law can use his power to generate high voltage energy; he can generate electrical energy to shock his opponents, and he can generate a blade of energy that he can use to damage his enemies internal organs without leaving an external wound.
Law is extremely skillful in wielding his Nodachi Kikoku, a sword about as tall as he is. Even without using his Devil Fruit abilities, Law is capable of fighting even a Vice-Admiral such as Smoker, as he is able to clash against his jitte with little effort and even block extremely powerful long range attacks such as Doflamingo's Overheat. In contrast to the ranged slashes of traditional swordsman, Law’s sword slashes don’t travel but simply provide the cutting effect while his spatial manipulation within his ROOM provides the range. Through spatial slicing, he can dismember people without harming them and attach separated parts in any manner he sees fit.
His swordsmanship combined with his Devil Fruit powers enable him to mutilate numerous people at once faster than they can react, easily defeating Kin'emon, a master of Kitsunebi-ryu and one of Wano's most powerful samurai in this manner. He easily defeat Tashigi, a highly skilled swordswoman of the Marines, severing her sword in two in one slash, as well as taking down Scotch and his giant knife in one swift move. He also managed to mutilate Trebol, an enormous man and also one of the strongest members of the Donquixote Pirates.
His greatest swordsmanship feats shown so far have been defeating Vergo, one of the strongest members of the Donquixote Pirates, where the wake of his slash was capable of cutting apart Caesar's laboratory and the surrounding mountains, and cutting a meteor in half.
He also managed to wrap the rope created by Donquixote Doflamingo's attack around his sword.
Law has shown great proficiency in Busoshoku Haki, as he was able to slice Vergo while the latter hardened his entire body with Busoshoku Haki and he could also block Doflamingo's Goshikito, which is powerful and sharp enough to slice Issho's meteorite and also took out a large portion of the palace, without getting injured at all.
During his battle with Smoker, Law was shown capable of bypassing the vice-admiral's Logia defenses thanks to his own Haki powers.
Kikoku is a large version of the typical Japanese sword type known as a nodachi. It has an oblong-shaped hand-guard coated with short white fur, sheathed in a black scabbard decorated by white crosses from the opening to the bottom, and with a small piece of red rope tied near its opening. Law appears to be quite skilled with it, being able to slice up targets from a distance (although this effect is attributed to his Devil Fruit power). Due to its size, Law usually carries this sword over his shoulder (in contrast to the other sword-wielding characters in the series, who either carry theirs on their hips or over their backs); yet in other times, he delegates one of his crewmates (namely Bepo) to carry this sword for him. Law was able to deflect Doflamingo's strings with his sword, which is noteworthy, as Doflamingo managed to effortlessly cut everything else so far.