Hi all! I play kog maw for a long time. In first he was total **** for me..but then i realized he is too good!:P You need to be a very good skill shooter for this build!

Pros:
Amazing ulti dmg
Amazing ulti range xD
Awsome mid game
Good late game
Best harraser EVER!

Cons:
Dies easily if they get to you
Just a bit mana problems early game (I solve it with clarity..)
I cant think of any more

I like to go utility for mana and cd's.. You can swap it for how you like.. But this is personnaly works best for me!:)

Now for the runes..I would go for Magic Penetration, CD's and Mana regen, but i use AS, MP and AP..i go for AS couse of early game farming..it sucks with Kog'Maw.. :)

Passive: Icathian Surprise
DONT forget to use this! It goes for true dmg and its awsome. I killd so many with these. I usually get focused in team fights late game..And die after 2 kills if i dont have flash. But i had quadra's with these!!!!

Caustic Spittle:
Early game i dont use it..just 1 lvl for help farming..nothing more..but late game this is very good nuke with E..Use it on tanks if they are only one left..couse it gets mr and armor lower!:)

Bio-Arcane Barrage:
Monster harraser..early game combine E spell and this..ull get about 1/2 of their hp in one harras if you place your E how it should be placed!

Void Ooze:
Again..deals very good dmg..and this is your skill for making surten ur attacks get them! Use this..W spell..auto attack while ultiing..

Living Artillery:

Main spell..insane damage for a 2sec cd..insane range for it! just this needes to be nerfed:P but it is kog maw! U need to be VERY GOOD skill shooter to land it! With practice and expirience u should have about 9/10 and if they suck at moving 10/10! :)

I start with Dorans Blade for help in farming..and extra hp is awsome:)..then go boots of speed and hex tech revolver..u can heal half of hp with this item and lvl 3 E spell..then go Sorceres shoes..u need that MP..Continue to 2 hextech gunblades..ur ulti scales with ap and ad..this is perfect for maxing it dmg..I 3shotted WW!..(Yes he was a noob but ok!xD)..Then madreds for AS and it passive..that dmg is cool for ulti!:)..Rylais for extra hp and slow..it is awsome..they just CANT run away!..And at last Frozen heart..just for some survivability and mana..

This depends on your playstyle..but i would get flash..Its ur escape..flash..E to them..and ruuun..some times go for ulti if ur faster!:)..1 slot u have..its on you..i go for clarity..i CANT maintain my mana..

I usually lane with my friend..he goes nocturne and i go kog'maw..In this combination..I harras and get 1/3 of minions..and he gets the rest..but mid is also VERY good..so if you are laning..Lane with a offtank or MAYBE support..but its not the best solution..it is mid or lane with meelee dps! :)

I wish you luck with this build..again i say..make your skillshots perfect! and they are done!:)
If thats just hungry..I frikin' DONT WANNA see him angry! :))))