As much as Brook normally goofs around on the ship engaging in acts of silliness with Luffy, he is still a formidable opponent. Due to his previous experiences and skills that he amassed from the days when the Pirate KingGol D. Roger was still active, Brook, in all respects, is a veteran pirate (though these attributes are somewhat downplayed by his overall demeanor, along with the fact that his isolation in the Florian Triangle seemed to have eroded his knowledge of modern society).
When Brook fights, his battles often have a comical element to them, including making a few of the members of his own crew fall asleep while fighting the Flying Fish Riders, playing dead halfway through a battle, or launching himself at an enemy with erroneous results. His childish personality occasionally hampers his effectiveness. Though he often gets scared easily by powerful enemies or the supernatural, he can be very calm and fearless to defend his crew, such as when he willingly sacrificed himself hoping to hold back a Pacifista and Bartholomew Kuma, and when he cleverly realized he could trick Giolla to defeat her. When he first met the Straw Hats, he quickly proved to be an asset to them during their encounters with Thriller Bark's many undead inhabitants.
Brook has demonstrated tactical ingenuity, as shown when he used his music to act like he was on Giolla's side, allowing him to regain his sword from her and defeat her. He also got the idea to store the copies of Big Mom's Poneglyphs inside his head before she confronted and later captured him. He is very good at working with others to execute plans in tandem, as shown when he took advantage of Pedro's distraction to get around his strongest opponents and enter the Room of Treasure. He also disguised himself as a clone of Luffy to take advantage of the chaos when Luffy crashed Big Mom's tea party, and he destroyed Big Mom's portrait of Carmel without being noticed.
He is shown to have a strong will, as he was able to withstand a burst of Big Mom's Haoshoku Haki.
Brook's skeletal body allows him to perform a wide variety of acts that would be impossible or fatal for a normal human to do. As long as his body remains solid and intact, he will live, and he can easily repair any bone damage simply by consuming milk. He can even survive having his head cut off, continuing to talk, smell, and see while it is detached. However, he is still capable of feeling pain. Due to his lack of flesh, Brook is resistant to lightning strikes and high and low temperatures. Brook does not age, as his body only consists of bones and he continues to grow stronger despite being 90 years old. He is capable of storing objects inside his skull, such as a Tone Dial and Poneglyph rubbings.
Brook's light weight as a result of his skeletal body makes him the fastest member of the Straw Hats. He can run across water without sinking, and jump extremely high into the air. Brook frequently uses his tremendous speed in battle, allowing him to take down opponents with attacks too quick for them to see. He was able to purify an entire horde of Soldier Zombies before any of them could react, and was capable of catching the Yonko Big Mom and her homies off guard with his attacks.
Though he has a naturally slim frame, Brook possesses an impressive degree of physical strength, being able to carry Luffy up to the crow's nest of Thriller Bark without slowing down. Despite not retaining any muscle tissue, it seems that Brook can still grow stronger over time, as he said to Ryuma that he has grown stronger over the span of the last five years. After two years of extensive training, Brook's strength has increased further, as the force he now applies in his swordsmanship is powerful enough to create flying slashes that can break thick ice from a far range and defend powerful strikes from a steroid-enhanced Zeo and Sheepshead of the Beasts Pirates.
Brook is a virtuoso musician who is extremely skilled in playing all kinds of instruments, particularly the violin, his favorite instrument. After he was separated from the Straw Hats, Brook picked up the guitar and, within two years, he became so highly skilled in the new instrument that he came to be regarded as a world famous rock star. At testament to this fact, his records in Tone Dials sold in the millions, and his fans during his final world tour stop in Sabaody Archipelago were either crying or fainting at his presence. Brook can masterfully play enchanting songs that are so melodious they can completely captivate even animals like Laboon, who used to sing along to Brook's music. In addition to singing and playing music, Brook is also a skilled composer, having composed songs such as "Bone To Be Wild" and "New World", which proved to be very fashionable among music fans and lovers.
Brook's devotion to music not only helped him to pass the lonely days during his long isolation, but also learnt to weaponize music for combat. His technique, "Nemuriuta Flanc" shows this, where he strums his violin with his shikomizue in place of a violin bow, creating a soothing tune that makes anyone who hears it immediately fall asleep.
His music also shows capabilities to change its listener's attitude and emotions, as when he was on Namakura Island, his music inspired the cult there to fight back against its invaders, the Longarm Tribe. During the fight with the New Fish-Man Pirates, Brook revealed that he has refined his musical skills to the point where he could completely change the mood and effectively hypnotize his opponents to believe they were at a festival. His opponents believed the illusion was reality and ended up using their cannons as fireworks. As a musician who mastered music temperaments such as rhythm, beat, and tempo, Brook has extremely sharp hearing that allows him to accurately distinguish sounds, as he was able to detect where Zeo was by the sound of his movements while the fish-man was invisible, even though Zeo was still difficult to locate through sound.
While he was still alive, Brook ate the Yomi Yomi no Mi, a Paramecia-class Devil Fruit that allowed his soul to return to his body after he died. This allows him to reside within a skeleton body, and he can even perform the functions he did when his body contained flesh and muscle.
Other than bringing him back from the dead, Brook's fruit initially seemed useless. However, after the timeskip, he discovered that he could exercise the power of his soul, which he discovered is what allows him to animate his body. He can separate it to move independently of his body. This leaves his body a lifeless husk, but as a spirit, Brook is capable of moving through walls and going to areas that would be impossible for him to physically reach, though he cannot grab hold of anything. He is capable of exerting his soul power to affect beings with weaker souls such as homies. This soul energy exudes coldness, called the "chills of the Underworld", and allows Brook to transfer this freezing aura to objects like his sword. With this aura, he is capable of freezing his surroundings, as seen when he turned the ground around him on Zou into ice.
Brook uses a type of sword called a shikomizue, a sword concealed inside a cane. He uses this sword in conjunction with his fencing skills and has had it for at least fifty years.
As a former battle convoy leader and pirate captain with years of experience in the Grand Line, Brook is a master in swordsmanship. Despite his usual goofy personality in battle, he is an extremely skilled Gentle Blade (柔剣,Jūken?) type swordsman who is able to dispatch numerous enemies at once with swift and precise strikes. His swordsmanship is a combination of classical fencing and iaidō.
Brook's Gentle Blade style is more focused on speed and precision while Zoro's style is more focused on power and thus uses a tremendous amount of physical strength. Brook was unable to defeat Ryuma no matter how hard he fought and while Ryuma only used a fraction of his power, he noticed that Zoro was able to defeat him at full power with only two of his swords, although Ryuma did say that Brook's protectiveness of his afro held him back somewhat. While at Sabaody Archipelago, two years ago, he struck a Pacifista using a high speed sword attack, yet failed to do much damage to it and had to be rescued afterward. However, when Zoro attacked the same Pacifista, the results were very different. He was able to keep up with what Zoro was doing while he watched the swordsman fight Ryuma, showing his sharp perception for swordsmanship. He works very well with Zoro, as they defeated a Flying Fish Rider together.
After the timeskip, Brook has named his sword "Soul Solid", due to him developing the ability to coat it with the aura of his soul, freezing it in the process, and anyone who comes into contact with it. He also claimed that the Longarm Tribe has helped him sharpen the sword. His power and skill in swordmanship has also increased to the degree where a samurai from Wano has commended his skill and he is also now able to use flying slashes as well, which were on par with Zoro's and Kin'emon's. Like Zoro, Brook can now cut materials that are harder than steel as he was able to cut down a dragon, whose scales are tougher than steel.
↑ 2.02.1One Piece Manga and Anime — Vol. 50Chapter 489 (p. 11) and Episode 381,
Brook reveals that he was the leader of the battle convoy of a certain kingdom before joining the Rumbar Pirates, and then his bounty as a pirate.