Early Game Generally in order. Weapon items for minions and souls. Last two items once you have grapple going
I500
I500
I500
I500
I500
I500
I500
Situational Flex Take 1 depending on enemy team comp. Not always necessary.
II1250
II1250
II1250
III3000
III3000
Mid Game Unordered. Take as you feel needed. Reach on Death Slam (4). Bullet Armor and Spirit Amor can vary in necessity based on enemy team comp. Once your late game mobility is going, feel free to sell Sprint Boots/Enduring Speed for more surviability.
III3500
III3500
III3500
II1250
III3500
III3500
III3500
II1750
II1250
II1250
III4250
III4250
Late Game Superior Cooldown on Death Slam (4). Reverb on Ground Strike (1)
III4250
IV6200
IV6200
Extra spirit if pulling ahead Uses a flex. More and more damage. Can melt minion waves and level 2 jungles with Flog (3)
I500
III3500
IV9700
Non-Core Weapon items Use shadow weave while already high up as grapple will activate the ambush.
I500
II1250
II1250
III3000
IV6200
Non-Core Vitality Items If you have space from not taking bullet or spirit armors. Choose based on circumstances. Heal Bane against Abrams, Infernus, etc. Bullet resist against Haze etc. Unstoppable to prevent Death Slam (4) interruptions.
II1250
III4250
II1250
II1250
IV6200
IV6200
Non-Core Spirit Items Surge on Ground Slam (1) as it improves Reverb. Curse for fed enemies you need to shut down.
II1250
III4250
III3000
IV6200
IV6200
IV6200
General Game Plan Become a fast moving ganker with strong map prescence. Use your grapple and stamina charges for map/fight movement, pursuits and retreats. Jump in and out of team fights with your mobility e.g. quickly jump into a 1v1, apply a burst of damage and dip out if you want to pressure elsewhere and feel confident in your teammate. Ground Strike becomes a very easy and fast way to clear creep waves, so do it often. Your main weakness is ceilings, do not take any fights indoors unless very confident you can win without most of your kit.
Grapple/Movement Tips Use your stamina for double jumps and air dashes for increasing distance and changing angles between using Grapples. If you're feeling extra spicy, you can wall jump off of buildings for no stamina, extra movement options, and even more style points. During team fights, constantly reposition to force the enemy to look in multiple directions, and anyone looking up into the sky at you is not looking anyone else on the ground.
Farming Your first source of farm is creep waves and any outdoors jungles which are easy to Ground Strike. With practice you can hit a good amount of the indoor farms with Ground Strike by aiming for doorways. The corner camps are the biggest pain to get and best left until Flog is really strong if you want to do them quickly. With enough spirit power you can clear entire minion waves with a single Ground Strike or Flog.
Death Slam Tips Always get above your enemies when ulting, this makes it much easier to grab them. Once cooldown is good, don't be afraid to use ult on lone players as it can really help you quickly demolish them or use it to get out of you can't win. In most cases, your ult can easily be followed by a Ground Strike for a simple combo. However some characters can react fast enough with abilities to avoid the damage, such as Mirage with his tornado. If you've used your ult on any of these characters, delay your Ground Strike and you may be able to catch them off guard. When defending your Patron, a simple trick is try and throw enemies into your respawn area and follow up with the Ground Strike combo. This gets them away from the objective, the towers in your respawn area will damage the enemies, and you and teammates will have the healing advantage while fighting in there. Movement slows or stuns are great here as the longer the enemy is in the respawn zone, the more damage they take from towers.
Description du Build
My own Lash Build. I'm no high MMR pro, but it works for me.
Broken up into Early, Mid and Late, with additonal categories for circumstances and a good amount of wiggle room.
Additional instruction and tips at the bottom.