Master yi was reworked twice already
once on patch 3.10 and once right after alpha ended on may 29, 2009.
He's had a ton of kit changes within those reworks and between them in smaller updates.
V6.10:
Meditate
AP ratio per second increased to 25% AP from 15% AP.
Wuju Style
Active's base damage increased to 14 / 23 / 32 / 41 / 50 from 12 / 19 / 26 / 33 / 40.
V6.8:
Highlander
Cooldown increased to 85 seconds at all ranks from 75 at all ranks.
Duration reduced to 7 seconds from 10.
Kills and assists time extension increased to 7 seconds from 4.
V6.6:
Wuju Style
Base damage increased to 12 / 19 / 26 / 33 / 40 from 10 / 15 / 20 / 25 / 30.
AD ratio changed to 25% Bonus AD from 10 / 12.5 / 15 / 17.5 / 20% AD.
V5.24:
Meditate
TOOLTIP CORRECTION: AP ratio is 15% AP not 30% AP.
V5.17:
General
Dance now scales with movespeed.
Alpha Strike
Fixed a bug where Double Strike and Devourer's Phantom Hit wouldn't reduce Alpha Strike's cooldown.
V4.5:
Stats
Base armor increased to 19 from 15.
V3.13:
Alpha Strike
Bug fix: Becoming untargetable will now correctly drop projectiles that were already in the air.
Meditate
Mana cost reduced to 50 from 50 / 65 / 80 / 95 / 110.
V3.10a:
Stats
Attack speed per level reduced to 2% from 2.75%.
Double Strike.png Double Strike
Fixed a bug where the second strike would damage targets even when Master Yi was blinded.
Meditate
Damage reduction increased to 50 / 55 / 60 / 65 / 70% from 40 / 45 / 50 / 55 / 60%.
Wuju Style
Passive attack damage bonus changed to 10% at all ranks from 7 / 9 / 11 / 13 / 15%.
Highlander
Now passively reduces the remaining cooldown for Master Yi's basic abilities by 70% on a kill or assist from 18 seconds on kill or 9 seconds on assist.
V3.10: remake
Stats
Health per level increased to 92 from 86.
Base mana reduced to 180 from 199.
Mana per level increased to 42 from 36.
Base armor reduced to 15 from 16.3.
Armor per level reduced to 3 from 3.7.
Attack speed per level reduced to 2.75% from 2.98%.
Double Strike.png Double Strike (Innate)
Every 4th consecutive basic attack, Master Yi will attack twice, dealing 50% damage on the second strike.
Alpha Strike (Q)
Master Yi becomes untargetable and dashes to up to 4 units, dealing 25 / 60 / 95 / 130 / 165 (+100% AD) physical damage and 75 / 100 / 125 / 150 / 175 bonus damage to minions. Alpha Strike can critically strike for 60% of Master Yi's AD.
Alpha Strike's cooldown is reduced by 1 second each time Master Yi basic attacks.
Mana cost: 70 / 80 / 90 / 100 / 110
Cooldown: 18 / 17 / 16 / 15 / 14 seconds
Meditate (W)
Master Yi channels for 4 seconds, gaining 40 / 45 / 50 / 55 / 60% damage reduction and healing for 30 / 50 / 70 / 90 / 110 (+30% AP) per second. This heal is increased by 1% for every 1% Health Master Yi is missing. The damage reduction is halved against turrets.
Mana cost: 50 / 65 / 80 / 95 / 110
Cooldown: 35 seconds
Wuju Style (E)
Passive: Master Yi gains 7 / 9 / 11 / 13 / 15% attack damage.
Active: Master Yi deals 10 / 15 / 20 / 25 / 30 (+10 / 12.5 / 15 / 17.5 / 20% AD) true damage on hit for 5 seconds. Wuju Style's passive bonus is lost while the skill is on cooldown.
Mana cost: 0
Cooldown: 18 / 17 / 16 / 15 / 14 seconds
Highlander (Ultimate)
Passive: when Master Yi kills a champion, the cooldowns on his basic abilities are reduced by 18 seconds (half for assists)
Active: grants Master Yi 30 / 55 / 80% attack speed and 25 / 35 / 45% movement speed for 10 seconds. If Master Yi scores a kill or assist while Highlander is active, Highlander's duration is extended by 4 seconds.
Mana cost: 100
Cooldown: 75 seconds
V3.5:
Double Strike.png Double Strike
Double Strike swing time now scales with Master Yi Master Yi's attack speed instead of being fixed at 0.6 seconds.
Fixed a bug where the second strike of Double Strike.png Double Strike could critically hit turrets.
V3.02:
Alpha Strike
Fixed a bug that caused Alpha Strike to appear available when it was on cooldown.
V3.01
Meditate
Total heal amount increased to 200 / 350 / 500 / 650 / 800 from 140 / 280 / 420 / 560 / 700.
Total ability power ratio reduced to (+200% AP) from (+400% AP).
Mana cost reduced to 50 / 65 / 80 / 95 / 110 from 70 / 80 / 90 / 100 / 110.
V1.0.0.153:
Alpha Strike
Initial cast time reduced.
Chance to deal bonus minion damage adjusted to 50% at all ranks from 20 / 30 / 40 / 50 / 60%.
Bonus minion damage adjusted to 260 / 320 / 380 / 440 / 500 from 400 at all ranks.
Meditate
Reduced the startup time before channeling.
Wuju Style
Cooldown reduced to 25 / 23 / 21 / 19 / 17 seconds from 25 at all ranks.
V1.0.0.152:
Stats
Base movement speed increased to 355 from 330.
V1.0.0.139:
Meditate
Mana cost reduced to 70 / 80 / 90 / 100 / 110 from 70 / 85 / 100 / 115 / 130.
Highlander
Fixed a bug where assists failed to reduce Alpha Strike's cooldown.
Duration increased to 8 / 10 / 12 seconds from 6 / 9 / 12.
V1.0.0.133:
Meditate
Fixed a bug where the ability power ratio was shown as lower than it actually was.
V1.0.0.129:
Alpha Strike
Mana cost reduced to 60/70/80/90/100 from 80/90/100/110/120.
Highlander
Mana cost reduced to 100 from 120.
V1.0.0.126:
Highlander
Fixed a bug where LeBlanc LeBlanc's Ethereal Chains.png Ethereal Chains could not snare Master Yi during Highlander.
V1.0.0.123:
Alpha Strike
Master Yi can now activate Wuju Style and Highlander while Alpha Strike is taking effect.
Master Yi will now attempt to attack the target after using Alpha Strike to blink to a champion.
V1.0.0.118:
Alpha Strike
Teleporting behavior improved to be more consistent when near walls. (this was removed in a hotfix because it caused Master Yi to always appear on the other side of the wall when using Alpha Strike on the Ancient Golem Ancient Golem).
V1.0.0.104:
Fixed a bug where MasterYiSquare.png Chosen Master Yi's sword was missing a glow.
V1.0.0.100:
Alpha Strike
Can no longer be cast while rooted.
Wuju Style
Tooltip simplified.
V1.0.0.96:
Added a glow to MasterYiSquare.png Chosen Master Yi's sword.
V1.0.0.86:
Double Strike.png Double Strike
Fixed a bug where it was represented incorrectly on death recaps.
Reduced the animation delay before performing Alpha Strike and Meditate.
V1.0.0.85:
Stats
Attack range increased to 125 from 100.
Double Strike.png Double Strike
Now deals a double strike on every 7th attack instead by percent chance.
Alpha Strike
Cooldown reduced to 18 / 16 / 14 / 12 / 10 seconds from 18 at all ranks.
Mana cost reduced to 80 / 90 / 100 / 110 / 120 from 90 / 105 / 120 / 135 / 150
Reduced total spell cast windup time.
Missile speed increased.
Meditate
Cooldown reduced to 35 seconds from 45.
Now ticks every 0.5 seconds instead of every 1 second.
Heal amount reduced to 140 / 280 / 420 / 560 / 700 from 150 / 300 / 500 / 750 / 1100.
Mana cost reduced to 70 / 85 / 100 / 115 / 130 from 80 / 100 / 120 / 140 / 160.
Armor and magic resist gained while channeling increased to 100 / 150 / 200 / 250 / 300 from 30 at all ranks.
Wuju Style
Cooldown reduced to 25 seconds from 30.
Highlander
Assists now reduce all of Master Yi's cooldowns by half of the base cooldown amount.
V1.0.0.70:
Highlander
Now applies an additive attack speed boost, rather than multiplicative. This change means Master Yi won't be as strong when using Highlander along with a second attack speed increase (such as items).
Now applies a multiplicative movement speed boost, rather than additive.
Attack speed boost increased to 40 / 60 / 80% from 30 / 50 / 70%.
V0.9.25.34:
Double Strike.png Double Strike
Chance to double strike modified from 12% to 10%.
Alpha Strike
Range reduced to 600 from 650.
V0.9.22.16:
Fixed an issue with Master Yi dying when using Alpha Strike with Guardian Angel item.png Guardian Angel on Baron Nashor Baron Nashor.
V0.9.22.15:
Stats
Base health increased to 530 from 480.
Health per level reduced to 86 from 88.
Damage increased to 55.7 from 48.7.
Movement speed increased to 330 from 325.
Damage per level increased to 3.1 from 1.775.
V0.9.22.7:
Stats
Increased movement speed from 320 to 325.
Meditate
Now increases armor and magic resist by 30.
V0.8.22.115:
Highlander
Movement speed increased from 30% to 40% due to movement speed soft capping.
Fixed a bug where Master Yi would sometimes lose an attack order after Alpha Strike.
July 10, 2009 Patch:
Alpha Strike
Now moves Master Yi to the target's location after the effect ends.
June 26, 2009 Patch:
Double Strike.png Double Strike
Proc chance reduced to 12% from 15%.
June 12, 2009 Patch
Wuju Style
Base damage increased to 15 / 20 / 25 / 30 / 35 from 10 / 15 / 20 / 25 / 30.
Cooldown reduced to 30 seconds from 40.
Mana cost increased to 40 from 25.
Active: bonus damage reduced to double from triple the damage of its passive.
June 6, 2009 Patch
Highlander
Attack speed bonus modified to 30 / 50 / 70% from 25 / 50 / 75%.
Movement speed bonus reduced to 30% from 35%.
Alpha Strike
Cooldown increased to 18 seconds from 16.
May 29, 2009 Patch: remake
(AND SO ON AND SO ON)