All of the Soul Reaper Captains in Bleach are among the series' most powerful characters, and have engaged in high-level battles over the course of the story. Some of their abilities are more straightforward than others, but Twelfth Division Captain Mayuri Kurotsuchi has emerged as having the most varied and interesting abilities among this cohort, even if he isn't the most powerful captain.
This variety, as well as his tendency to fight opponents with his brain first and his Zanpakuto second, makes Kurotsuchi's battles some of the best in Bleach.
Who is Mayuri Kurotsuchi?
Kurotsuchi is a sadistic mad scientist with a love for experimenting on live subjects, himself included. His division which is home to the Shinigami Research and Development Institute. Kurotsuchi runs it with an iron fist and has even gone so far as to turn underlings into human bombs to suit his whims. The powers that be in Soul Society put up with these evil acts because Kurotsuchi is also one of the most brilliant minds in Soul Society. Only Sosuke Aizen and Kisuke Urahara rival him in sheer intellect.
In battle, Kurotsuchi regularly uses his Zantspakuto, Ashizogi Jizo, which suits his personality well. The blade is capable of inflicting paralysis on those it cuts while keeping the sensation of pain intact, allowing Kurotsuchi to torture them. His Bankai (a Zanpakuto's strongest form), Konjiki Ashizogi Jizo, takes on the form a baby-headed giant caterpillar, which can emit poison gas and has hidden blades. It can also swallow enemies whole.
These abilities are powerful on their own, but Kurotsuchi has even more tricks up his sleeve. Firstly, in addition to experimenting on other people, he has modified his own body extensively. These modifications include being able to extend his left arm like a hookshot, hiding a hidden blade attached to one of the nodes on his head, the ability to blend in with his surroundings via camouflage, and the ability to liquefy and thus protect himself from harm in a battle he can't win. In his battle against the power Arrancar Szaelloporo, Kurotsuchi even went so far as to give himself extra copies of all of his organs in case they were damaged.
If all of that wasn't enough, Kurotsuchi is a skilled inventor with a variety of contraptions that aid him in battle. Among these is the Hojiku-Zai, a regeneration serum which allows Kurotsuchi to regrow lost limbs and body parts, although this causes him pain. He is also a master chemist, and has on multiple occasions crafted unique and dangerous drugs which alter his opponents' perception of reality. In the Thousand Year Blood War arc, Kurotsuchi extensively modifies his Bankai (something no other Soul Reaper has done) to give it an entirely new and more powerful form.
What Makes Kurotsuchi's Battles Memorable
As of now, Kurotsuchi has only had six major battles in all of Bleach, two of which are non-canon (against the Bount Sawatari and the mod soul Kageroza Inaba). In all cases however, these battles stick out as some of the best in Bleach due to Kurotsuchi's unpredictability. He has a plan for nearly everything, and usually defeats his opponents in extremely creative ways after observing them first. Kurotsuchi's first battle was against Uryu Ishida, and was the only canon battle he lost. This battle shows off several of Kurotsuchi's modifications, but is especially focused on his Zanpakuto, and is also the first time in Bleach that a Bankai was unveiled. Kurotsuchi outclassed Uryu in nearly every respect, forcing the young Quincy to remove the limiter on his powers to use it all at once. This left Uryu to temporarily lose all of his abilities in exchange for seriously damaging Kurotsuchi. Kurotsuchi liquefied in order to heal and left the battle.
Kurotsuchi's second canon battle was against Szaelloporo Granz, a powerful Arrancar scientist. This clash between minds is one of the strangest in Bleach. Kurotsuchi and Szaelloporo take turns outwitting each other with different inventions and abilities. The former survives thanks to preparing spare organs and eventually tricks Szaelloporo into ingesting a Superhuman Drug that makes his thoughts move so fast that his body can't keep up. This speeds up Szaelloporo's mind to the point that mere seconds seem like an eternity, and render him unable to react to Kurotsuchi's blade piercing his heart.
Kurotsuchi engages in two battles in the Thousand Year Blood War Arc. In the first, he participates in a greater battle against the Quincy Giselle and several zombified Soul Reapers, including three Captains, one Lieutenant, and also a zombified Quincy, Bambietta. Kurotsuchi fights them alongside Ikkaku and Yumichika of the Eleventh Division, as well as four Arrancar he revived. Once again, Kurotsuchi uses a variety of drugs to overcome these threats and eventually take control of the zombies.
His final battle so far is against the Quincy Pernida, a giant hand that controls others with its nerves, an ability known as The Compulsory. Mayuri modifies his Bankai to have layers of surface nerves that shed off each time Pernida tries to control them, rendering it immune to its abilities. Every time it seems like Kurotsuchi should lose a battle or his life, he always figures out some insane way to cheat death and stump his opponent. This unpredictability and his large arsenal of drugs and inventions make it much harder for fans to predict how Kurotsuchi will operate in battle compared to characters with a relatively simple moveset, like Ichigo Kurosaki. That distinction makes Kurotsuchi's battles especially engaging.