Hello Summoners,
My name is Operimity, But you can call me Gus, Im a 1200+ elo player with around 3 years of experience in the league. The majority of my experience in the League is spent at solo top with other champions such as Jax,Nasus,Teemo and most notably Irelia. Before you delve deep into this guide i advise you to grab a pen and paper and get ready for some awesome content!
Gimme' a thumbs up!

As a young teen, Lee Sin was intent on becoming a summoner. His will and dedication were unmatched by any of his peers, and his skill drew the attention of Reginald Ashram, the League's High Councilor at the time. While studying at the Arcanum Majoris, Lee Sin became frustrated with instruction paced for the other students. He spent his free time researching the nuances of summoning in hopes of graduating sooner. He made amazing advances in his arcane studies, surpassing all other students. By all indications, he would have become one of the League's greatest summoners were it not for one terrible mistake. Too impatient, he attempted to test his ability by summoning a beast from the Plague Jungles. What he summoned instead was a young boy, but not in one piece. He barely had time to look the boy in what was once his face before the jumbled human mass fell lifeless to the floor. A League investigation later revealed that the boy's entire village was obliterated by feedback from the ritual.

Lee Sin's talents were so promising that the League was willing to overlook the incident, but he could never forgive himself. He left the Institute and journeyed to the Shojin Monastery for eternal repentance, swearing never to practice magic again. Years later, hoping to atone for his crime with martyrdom, he set himself ablaze as a protest of the Noxian occupation of Ionia. He remained alive in this state, enduring searing agony for weeks. His actions paved the way for a League match wherein Ionia prevailed, but by the time he was doused, his eyes had been burned completely from their sockets. Hailed as a savior, he was reborn, and his will to act invigorated. He joined the League of Legends to continue his atonement with sweat and blood, a true monk's only possessions.

''The actions of one may sunder the world, but the efforts of many may rebuild it.''
-- Lee Sin

PASSIVE:
After using an ability, Lee Sin's next 2 basic attacks within 3 seconds gain 40% attack speed and return 15 energy each.
Sonic Wave RANGE: 975 COOLDOWN: 11 / 10 / 9 / 8 / 7 COST: 50 energy
ACTIVE: Lee Sin shoots a wave of sound in a line, dealing damage to the first enemy it hits and revealing the enemy for 3 seconds. If Sonic Wave hits, Lee Sin can cast Resonating Strike within the next 3 seconds.
PHYSICAL DAMAGE: 50 / 80 / 110 / 140 / 170 (+ 90% bonus AD)
Resonating Strike RANGE: 1100 COST: 30 energy
ACTIVE: Lee Sin dashes to the enemy revealed by Sonic Wave, dealing damage including 8% of the target's missing health. Minions and monsters take a maximum of 400 damage.
PHYSICAL DAMAGE: 50 / 80 / 110 / 140 / 170 (+ 90% bonus AD) (+ 8% target's missing health)
COMBINED DAMAGE: 100 / 160 / 220 / 280 / 340 (+ 180% bonus AD) (+ 8% target's missing health)
Safeguard RANGE: 700 COOLDOWN: 9 COST: 50 energy
ACTIVE: Lee Sin dashes to target ally, he and the target each gaining a shield that absorbs a certain amount of damage. Each shield dissipates after 5 seconds if not already destroyed. If either shield is broken, Lee Sin regains half of the energy cost. Lee Sin can cast Iron Will within 3 seconds of using Safeguard.
SHIELD: 40 / 80 / 120 / 160 / 200 (+ 80% AP)
Iron Will COST: 30 energy
ACTIVE: For 5 seconds, Lee Sin gains armor, life steal, and spell vamp.
ARMOR: 10 / 15 / 20 / 25 / 30
LIFE STEAL, SPELL VAMP: 5% / 9% / 13% / 17% / 21%
Tempest RANGE: 175 COOLDOWN: 10 COST: 50 energy
ACTIVE: Lee Sin smashes the ground, dealing damage to all nearby enemies and revealing them for 4 seconds. If Tempest hits an enemy, Lee Sin can cast Cripple within the next 3 seconds.
MAGIC DAMAGE: 60 / 95 / 130 / 165 / 200 (+ 100% bonus AD)
Cripple RANGE: 500 COST: 30 energy
ACTIVE: Lee Sin cripples all enemies revealed by Tempest reducing their movement and attack speed. The movement and attack speed recover over 4 seconds.
SLOW: 30% / 37.5% / 45% / 52.5% / 60%
Dragon's Rage RANGE: 375 COOLDOWN: 90 / 75 / 60
ACTIVE: Lee Sin deals damage to a target and knocks the target back 1200 units. Enemies the target collides with take the same damage and are knocked airborne.
PHYSICAL DAMAGE: 200 / 400 / 600 (+ 200% bonus AD)

PROS:
- Awesome Mobility.
- Good burst damage.
- Good sustain with W.
- Great initiator.
- Beast single target damage.
- Can be played top, mid or jungle.
CONS:
- Fades off late game.
- Levels 1-6 are quite difficult
- Extremely hard to catch up if you are in a deficit.
- Susceptible to CC
- Screwed against heavy defensive skills.