Yasuo was regarded as a brilliant pupil at a renowned Ionian sword school and was the only student in a generation to master the legendary wind technique at a younger age than ever attained before.
Hecarim is a master of virtually every form of combat and warfare known to man
Yi has dozens of years of experience in the art of Wuju, a martial arts style that requires an immense amount of patience and strategy, centered around analyzing the opponent for any openings or weaknesses before killing them with a single cut, and even before Yi mastered Wuju he was considered one of the most skilled practitioners of the martial art, being described as never attacking until landing a strike on his opponent was absolutely guaranteed.
Rengar is highly regarded as one of the most killed hunters in the world, surpassing even his adopted father, who was considered a legendary hunter, and his father by birth, who was so skilled a hunter that he was crowned chief of the Kiilash.
Katarina and Talon are widely accepted as the second and third greatest knife wielders in the world, with the first being Katarina's father who trained them both.
Garen is Katarina's equal in combat and regarded as one of the greatest swordsmen in the kingdom of Demacia
Lee Sin is a master of Ionia's unarmed martial arts and is skilled to the point that just by listening to the movement and breathing of three men he was able to determine that one had lung disease, one had a weak heart that would give out in less than a year, and one had an injured spine that forced him to walk slightly more on his left side
Leona was taught how to fight as soon as she was able to walk and spent her entire life training in combat, mastering the sword and shield as a very young age and spending most of her childhood fighting monsters and supernatural beings that resided on Mount Targon. Her skill is great enough to match Pantheon, who had devoted even more time to mastering martial combat than her, to the point that no one on Mount Targon was sure who would win when they fought. After she was inducted into the Solari she spent year honing her already fearsome skill even further.
Nasus' grasp on military strategy and logistics ensured he became the youngest general in Shuriman history, quickly gaining him a reputation for being able to remain twelve steps ahead of his opponents at any given time, being able to predict their movement and reactions, as well as pinpoint the exact moment to push the attack or pull back, guiding the armies of Shurima to countless victories
Wukong mastered Wuju Style in a very short time period, an art that took Master Yi several dozen years to master, and became skilled in the art to the point where he was able to outsmart Yi on more than one occasion
Shen, while in a crowded, busy ballroom, Shen was able to instantly deduce that Zed was half a finger length too far way for him to be able to attack the moment he saw him, despite the latter being in a disguise and attempting to avoid detection. He also played a major role in capturing Khada Jhin, who is so skilled with his rifle that he is unhindered by a mask that both constricts his breathing and removes his depth perception, managed to evade capture by the Ionian people for years, and outsmarted Wuju masters
Xin is hyper-analytical in combatant and was able to easily defeat an army of fifty men on his own and then went on to defeat another man who accomplished the same feat but without being allowed a weapon (Xin was unarmed, the other man was not)
Kayle has over ten thousand years of combat experience fighting and winning a war on her home world against an army of immortal warriors as strong as herself
Jax is more skilled than all of these guys