Q decrease enemy DEF/Magic resistance
(Just to focus Q)
continence use W for farming
(enemy's go damage dealing your W cooltime)
Do use E enemy's path
core item = only needs, select item = some situation
Guinsoo's Rageblade = 1st core item
Berserker's Greaves = need boots
Runaan's Hurricane = 2st core itemif they exist zed, you go
and buy last(6st) -> 
Blade of the Ruined King = 3st core item(This item suitable kogmaw's W : AS, percent damage, active slow and deal)
---------------------------------
5st select item
Phantom Dancer = master yi, vayne and such enemy team have 1vs1 strong champ(this item decrease damage 12% and have highest AS between AS items)
Sterak's Gage = enemy's very strong and target me, increase the viability
Lord Dominik's Regards = If there are a lot of enemies tanker, this item amp deal for tanker
Rapid Firecannon = my team overwhelming win (not better than Phantom Dancer:this item 15% low AS than Phantom Dancer)
6st select item(if you go
, purchase
)
Infinity Edge = if you go Phantom Dancer, crit percent over 60%. and Infinity Edge increase 50% crit damage, 20% crit chance and ad +65. hard carry item
Banshee's Veil = enemy's More than 2 AP champs, you consider this item.
Guardian Angel = enemy's team exist zed, talon, akali... etc assasins champion, you consider this item