Helloooooo, my name is Norswedish and i'll hopefully make you a little better at playing the monster from the abyss named Kog'Maw.
I got inspired to make this guide since i've played a lot of Kog'Maw as a hybrid AP/AS champ and the new changes to his abilities and his playstyle makes hybrid an even better build for him.Custom skin not made by me!!!
Get it here: http://leaguecraft.com/skins/5011-aperture-kogmaw.xhtml

Pros:
- Long range
- Easy to build
- Farms great
- Can 1v1 mostly anyone
- Fun to play
- AWESOME PASSIVE! BOOOM!

Cons:
- Very squishy
- Slow
- No real ecape mechanism
- Targeted (not a real problem if you stand at range)

This is the one area that can really vry from player to player, but the 9/0/21 build with AP, CDR and magic pen. And getting what you need and want in utility is nice.

I have chosen these runes based on the role Kog'Maw has in teamfights as quite a passive champion that stays in the shadows until a teamfight erupts where he starts raining hell upon the other team.

Greater Mark of Magic Penetration:

This is a standard rune used on most AD champions, so i use it on Kog, Purely because Bio Arcane and Madred's are both magic damage. Good runes!

Greater seal of replenishment:

To put it in short terms, Kog has some mana issues, it's nice to be able to spam your ultimate and not having to leave lane to recover mana every time, and spend your gold on items instead of mana pots

Greater Glyph of Mana:

Kog has some mana problems early game, low base mana and pretty hig base mana cost on early game abilities compared to mana pool may cause you to not have that extra Q to secure the kill

Greater Quintessence of Cooldown Reduction

: I was very torn on the quints, because there are so many viable ones i really couldn't decide. But i went with the CDR ones, but you should use the ones that fit your playstyle

Flash

: Use it!!! Kog'maw is very slow and a real gankable champ so using this spell is your best bet to escaping ganks and also for chasing

Ghost

: This is also a very viable summoner spell, good for chasing and escaping

Teleport

: Whatever floats your boat. Nice to have if a tower is getting pushed from a huge wave of minions and you are a little low on farm

Exhaust:

I wouldn't use it, you're usually too far away from the other team to use it...

Ignite:

Same category as Exhaust

Heal:

Nice to have but not THAT good...

Clarity:

Also a nice choice to a regularily mana starved Kog, but i'd rather get blu buff

There are some others aswell but i see these as the ones that have meaning and are utilizable by Kog

Start off with a basic

Doran's Blade

to start you off eith some damage and health
From there get

Boots

and some

Health Potion

If you can afford it buy

Berserker's Greaves

Now farm as much as humanly possible, gank the other lanes, get some kills and rush both

Malady

and

Madred's Bloodrazor

This is where the build's vary

Banshee's Veil

Nice item to get, some survivability is important

Guinsoo's Rageblade

Takes some time to earn stacks but really worth it, can require some skill to be able to utilize

Hextech Gunblade

This item is very expensive but great for finishing off you'r build, sell you'r dorans, buy a Hextech Revolver and build from there

Other choices

Nashor's Tooth

AD&AS, very good for this build, but i feel like thee are better item's to get

Phantom Dancer

Great item for Kog, AS and run speed helps out a lot, but the crit is kinda useless and there are better substitutes, but if you want it, go for it ;)

Lich Bane

This is a very attractive item, i love it, both the stats and the passive. Run speed at the same time as it gives MR, move speed and AP. But it soesn't synergize really well with the build because of the mediocre AP. But it can work really well with a

Nashor's Tooth

Early Game: Kog can be really annoying in a solo lane, with harasses that outrange most champions, and at level 6 another long range ability that hurts real bad for usual squishy solo laners. Be sure to get Sight ward's so you don't get caught pushing tower.
You should do basically the same in a duo lane, harass as much as possible but remeber to conserve your mana for a champion fight and not spam your abilities.

Mid game: This is what separates a good Kog from a bad Kog. At this point the game should be in about 15 minutes and you should be past your Malady and also some kills or ganks (This is all ideal though). Now to get some buffs, get your teams jungler or tank(you should have a jungler) to tank the monsters for you and get red/blue buff, both are equally important but woth a few differences.
Blue: This makes all your spells spammable but not infinately spammable, a nice little rule to have is use your Q,W,E when they are up. And use

Living Artillery

up to 3 stacks, then let it cool down
Red: Use this to gank/chase your opponent. Since you have such a huge range with your

Bio-Arcane Barrage

you should be able to kite almost any champ.

Late game: Congratulations! If you have 150-200 Minion kills, and somewhere around 2-5 kills you should now be a killing machine. As long as you have

Berserker's boots, Malady and Madred's Bloodrazor

you really hurt, even the opposing teams tanks will fear you, because of your runes and Malady you should have enough Magic Pen to take them down (But focus the squishy champs first).
Stay at max range, keep your

Bio-Arcane Barrage

up, spam

Living Artillery

and you should be fine. Play smart, kill dragon, take baron buff, take the neutral buffs, and enjoy being a killing machine.

This buld isn't completely finished, i still want to make some changes and make this guide the best Kog'Maw build there is.
Give me you'r thoughts down in the comments so we can all get better at playing that little demon