I'm Kog Bot and have been playing kog'maw for the past 3 seasons. I fell in love with his kit and his insane late game damage. Nothing is more satisfying than watching your opponents tremble as you slowly grow more deadly as time goes on. I hope you enjoy my guide. Feel free to shoot me questions if you have any. I hope to update this guide quite often. Thanks!

Kog'maw is still pretty good after 6.17. His two hardest meta match ups in lane were nerfed. Jhin and Ashe could abuse kog'maw in lane. Often times you felt helpless with these match ups. These nerfs will help bring in some new picks that kog'maw should be able to handle.6.18 Patch Notes
BANS:
Yasuo, Hecarim, Irelia, Zed, Blitz, Jhin

Changes Coming
Kog'maw is getting significant changes soon. 6.19 is reverting kog'maws rework. In my opinion the current pbe changes are significant nerfs. RIP on-hit build.
Dev Board
Developer Discussion
PBE Changes
PBE

Before we get started let me start off by saying kog'maw is not the champion for you if you are very aggressive or lack patience. I play kog very patiently throughout all phases of the game. I often times receive ridicule from my team about how passive I can play. To me kog'maw gameplay is a timing game. I win most games when I play it patiently and my team embraces that play style. Patient game play does not mean you don't go aggro. It simply means you know when and when not to fight.

Early Game:
Unlike many champions, kog doesn't need kills in lane to win. All you need to do is make it to mid/late game without feeding. In most match ups I cs for a good 15 or 20 minutes and avoid too many exchanges. Every match I make it very clear to my support that I will play passive early. This prevents circumstances where your support lands an ability and dives all in when you are unable to capitalize on the play. Call for ganks if the opportunity arises and you can probably pick up a few early kills. Avoid 2v2 or 1v2 scenarios bot in most cases.

Mid Game:
At this point you should have a wits end, hurricane and some boots. Just these items alone make you a huge threat. Start to step up your aggression. Look to take towers and objectives. You are now at the point where you can win most fights bot if your support lands a good stun or alternate ability.

Late Game:
The dream, late game is where you shine. Don't get cocky. You are still a weak little thing. Use your team as meat shields and instruct them to protect you at all costs. If you can keep a distance between the enemy and you in team fights it's gg. The majority of my losses come from the unwillingness of my team to value my damage. They engage fights when I'm not there and leave me alone in team fights. A BIG part of successful kog game play is being open with your team. Be a shot caller because you need them more than they need you. Use your insane damage late to surprise your enemies. DO NOT focus the adc in fights unless they are very close. Keep your distance and shred all nearby targets while being aware of any assassins.