Lee Sin
Their Heartbeats Quicken
Lane harassment and consistent damage output.
Domination
Burst damage and target access
Dark HarvestDamaging a low health champion inflicts
adaptive damage and harvests a soul from the victim.
Sudden ImpactDamaging basic attacks and abilities deal bonus true damage to enemy champions after using a dash, leap, blink, teleport, or when leaving stealth.
Grisly MementosCollect 1 memento on champion
takedowns , up to 18 total.
Gain 6 Trinket Haste for each collected.
Relentless HunterUnique
takedowns grant permanent out of combatMS .
Precision
Improved attacks and sustained damage
TriumphTakedowns restore 5% of your missing health and grant an additional 20 gold.
Legend: AlacrityTakedowns on enemies grant permanent Attack Speed.
Adaptive Force
+9
Adaptive Force Adaptive Force
+9
Adaptive Force 
Health Scaling
+10-180 Health (based on level)
Why Dark Harvest
Dark Harvest is quickly becoming a prominent jungle keystone as it allows you to front-load a lot of damage on incoming ganks to help secure an easy kill.
Why Sudden Impact
Dashing with either [Q] or [W] makes for an easy way to get a quick 10 Lethality, giving Lee plenty of early game kill potential.
Why Grisly Mementos
Grisly Mementos is especially good on junglers as it allows you maintain high vision control throughout the entire map.
Why Relentless Hunter
Lee Sin is all about his positioning and getting into the lane for a gank as quickly as he can. The extra Movement Speed from Relentless Hunter plays a big role in keeping you on the map and relevant everywhere.
WhyTriumph
Triumph's burst of bonus healing after a kill/assist allows you to get away with some risk tower-dives and survive so that you're able to snowball a lead to victory.
WhyLegend: Alacrity
The extra Attack Speed from Alacrity is fantastic, especially in the early game, for empowering your jungle clear and passive auto-attacks to keep you healthy. Against heavy CC comps be sure to take Tenacity.