I decided to max out simultaneously Void Ooze and Bio-Arcane Barrage since they work like bread and butter with each other, and leave out Caustic Spittle for the end since it doesnt cooperate with the other spells early game. Of course, I level up Living Artillery whenever I can.

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• : Let's you deal almost true damage early game. If your enemy team tend to focus you with CC switch them for Mercury's Treads late game.
  
• : Let's you stay in lane forever and also sygergizes well with Archangel's Staff.
  
• : I don't even need to explain, all I can say is that it let's you have around 950 ap late game.
  
• : Let's you spam your ultimate without going out of mana early. Also gives a sh*tload of AP.
  
• : Just throw an AA between every spell you cast and you'll be dealing crazy damage.
  
  

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In Laning phase, you should focus on two important things: Last hit as much minions as you can, and zoning the enemy champion. While doing so you should keep in mind a few tips:

+ Always avoid minion aggro. If the enemy minion wave has more pressure than yours, don't harrass unless you're going for the kill and That you're sure to survive after getting him. You have no sustain so you will end up zoning yourself if you harass unconsciously.
+ When you are harrassing/zoning the enemy champion, keep in mind that their jungler will certainly come to gank your lane to free his friend from your pressure, so never overextend without wards or while Flash is on cooldown.
+ While playing AP Kog'Maw, I found out that there's a specific moment when I often get a kill if your jungler is a bit tanky/not squishy or has insane gap closing mechanics such as Lee Sin or Maokai. The way to always snap a certain kill is that, after zoning and harrassing your enemy, his friendly jungler comes in to help. There's a 90% chance he will burn his Flash to close the gap on you and help his jungler to kill you after the jungler engages you. What you do is throw a Void Ooze in front of you so they can't chase you, and if necessary Flash away. After a fail gank the enemy jungler will guard the mid lane for the enemy mid champion to recall and come back. When t jungler's gone and the enemy mid is back, Now is the time you go for the kill: pop your HP/Mana pots and go aggressive on him, just spam all the spells and make sure you never miss. The thing is, he won't recall back when he falls to low HP because he just recalled a while ago and he wont risk losing more farm/exp. Now all you have to do is towerdive with your jungler, immediately Void Ooze+ Ignite if he fights your jungler back, or Snipe him off with Living Artillery while he runs back to base. Make sure your jungler is good and knows what he's doing.


In teamfights, your job is easy and simple: Try to hit as many enemies as possible with Void Ooze, focus with Bio-Arcane Barrage and Caustic Spittle along with AA with Lich Bane procs between spells and Ignite their carry, and constantly throw a Living Artillery between AA. If you are winning the teamfight, be ready to snipe off the runners/flashers with your ultimate and get the well-earned ace.

+ Always try to stay away from enemy spell/AA range since you have much more range. If they try to focus you and you drop low health and you know you'll die a certain death soon, go in the middle of the lot, spam as much ultimate as you can and explode in the middle of the teamfight.

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Well this is it ! I hope this wasn't too long to read, I tried to keep things simple. I also hope you enjoy playing this champ as much as I did. I am expecting your feedback my friends! And i'm looking forward to improve as I could use a bit of help from you guys with that =P

If you found this guide very helpful, please Upvote and +rep me as a lot of time was put in this and I would like to see some encouragements and motivations to help me make more guides in the future. If you do downvote for any reason, please let me know why in the comments section below and I will do my best to rectify my errors.

At last, i've managed to collect some screenshots of successful games from solo queue gaming with AP Kog'Maw these last few days. I never went negative with him in these last 16 games I played but I only won 12 of them. After all, it's a team game, and one can't do a whole team's job ;) Send me yours and i'll upload them along with mine gladly.


Also I wanna thank these people who helped me a lot through their templates and guides to make this guide, thank you guys. It was jhoijhoi who mentionned them in her template and I used her template so they deserve credit too.


PsiGuard
LameoGamer
Bloofyre
ShadowNet
SirSpank
Meridianprime


17/07/2012: Detailed the item build section.
16/12/2012: I was about to archive this guide but when I saw the good feed-back I decided to update it for S3, although there wasn't much to change except Masteries.