So my mistake buying this champion. Current rotation is a ton of heroes with gap closers and disables. But I found out that for some reason Riot didn't change the default build for Kog'Maw after his nerf. I couldn't find anything online either.
MLDzXnRRR1 votes
DeathBurst1 votesNope... Infinity Edge is bad, Rapidfire is okay but there are better options, Last Whisper is not even a full item, and most of the time it's better to take another AD item with lifesteal than Guardian Angel.
LynXerf1 votes
Best but you can also take 
and pick one of the following 
On-hit is superior for Kog. His AD scalings are non-existant and his AS buff does 50% damage, but 100% of on-hit damage. 4-5 attack speed applying BORK, Rageblade and Wit's End is great, anything else feels sub-optimal.
Mr Vulcanator1 votesWhat about starting items? And durability so I don't die if a scuttle crab glares at me? Why shouldn't I buy AP items and spell vamp?
LynXerf1 votes[{quoted}](name=Mr Vulcanator,realm=NA,application-id=3ErqAdtq,discussion-id=iWJ1T4L9,comment-id=00020000,timestamp=2015-12-15T16:02:13.760+0000)
What about starting items? And durability so I don't die if a scuttle crab glares at me? Why shouldn't I buy AP items and spell vamp?
Well most of all, never go anywhere by yourself. Always follow teammates around and stick behind them, moreso than any other champion in the game. Don't try anything by yourself. Then when things kick off, you can step into someone else's fight and end it in an instant. THAT is more important than durability.
Early game get double dorans if necessary and then go Rageblade or BORK first item.
Later game wits end, BORK and health from BC or TRI will give you some resistance to being deleted.
DeathBurst1 votesBecause spell vamp is for spells, and you don't deal damage with your spells, not really. AP Kog'maw is kinda viable, but midlane usually, not bot with a support.
And ADC usually only build lifesteal as defense. Add a Bloodthirster or a Mercurial to your build, for instance.
For starting, if you are not completely counter-picked in lane, try 
otherwise good ol' 
is still a sure value.
DeathBurst1 votesI'd recommend finding room for a 
somewhere. Probably instead of Lord Dominik. It is THE standard item for ADC with on-hit builds (because the secondary bolts deal 50 % AD, but 100 % of on-hit, just like Kog AS steroid).
Rebonack1 votesDon't listen to the people suggesting Hurricane. They're deceiving you.
The two most effective ways to build Koggy are 
followed by situational items.
OR
In both cases you want to start with a Doren's blade.
Kog can either roll as a ranged Juggernaut who hurts way too much to ignore, or he can go balls to the walls AP Marksmen if your team has good peel and the enemy team has picked no one with gap-closers for some obscene reason. Lug around a Blue Elixir with you late game and pop it when you need a tower to evaporate.
Mr Vulcanator1 votesWhat do you suggest for situational items and HP recovery? Would Liandry's Torment be good?
Rebonack1 votes[{quoted}](name=Mr Vulcanator,realm=NA,application-id=3ErqAdtq,discussion-id=iWJ1T4L9,comment-id=00030000,timestamp=2015-12-15T17:03:10.833+0000)
What do you suggest for situational items and HP recovery? Would Liandry's Torment be good?
Kog's base damage isn't really strong enough to justify torment.
If your team is lacking in a healer to top you off, you can snag Gunblade and Bork. Otherwise you can go with Cleaver and Bork. Or Mercurial. Or Maw. Or even straight Tank items if you have a Soraka following you around. The big thing to keep in mind with TanKoggy is that even though your damage will be a bit lower than the glass builds, you're four times as durable.
Most people don't except Kog to be able to take a hit. You'll have a lot of assassins that you can straight-up duel try to dive you and get killed as a result.
Bonipherus1 votesIf you are going for a siege/poke-heavy ap kog then yes 
is very good. Your ap ratios are very low and Liandry's damage over time will add more to your poke damage against a healthy target more than any other item. It essentially will work to wear your opponents down to a level where the double/triple damage of your ult will kick in more efficiently.
The 15 flat magic pen also is fantastic for dealing more damage and is really overlooked by people who don't understand the math. Flat penetration is calculated after % penetration which means getting a void staff and some flat pen runes is very good at dealing tons of damage to your enemies.
Also note that the passive proc from 
will spread the Liandry's burn to everything it hits. These items are made for poking your enemies down.
Items should be 
for a highly versatile and effective AP Kog'Maw build. Work in a when against teams that aren't letting you poke as much.
Wolfram Oxford1 votes 
Wolfram Oxford1 votesfull ad is better than on hit since the ratio on the aa is more than 0.5
Bonipherus1 votes overcomes so much of your early game weakness and synergises with your kit so well that it should be rushed. Gives a great on hit passive for kog, both ad and ap, and the most attack speed of any single item
on hit passive is twice as effective on kog, active helps keep you alive, and a good chunk of attack speed.
gives even more ap as well as another on hit passive with scaling. also comes with a lot of attack speed.
will let you heal off of all of your on hit damage while giving ad and ap. This item will heal you more than even a bloodthirster. Active can also be pretty useful.
is an item I do not recommend. Kog is extremely immobile (perhaps the least mobile in the game now) and you should not be in a position where you can hit 3 champions at once. Theoretical damage output is very high but you'll have to almost completely compromise your safety to achieve this damage. Your damage when only a single enemy is in range (the more ideal scenario) will be less with this item compared to another attack speed/on hit item. Only buy when in and/or against certain team comps.