Play by the Kog rule “the trade ends before W does”: Q -> W auto(s) -> back out is often the whole win, because borrowing range for one to three clean autos is better than trying to cash every second of Bio-Arcane Barrage.
Treat your support as extra seconds on W, not just generic lane help—Kog's best lanes are the ones where peel or reliable CC lets you spend the timer shooting instead of spending it trying to gain access.
Kog is unusually recoverable for a hypercarry, so from behind the usual mistake is forcing a roam or hero play instead of preserving the game for one more real W fight, which recent data shows he survives into better than many similar bot carries.
Press W when you already know what the next few seconds look like. In lane, that usually means the enemy has just used the spell that reaches you, your support has started the trade, or you have a clean Q and room for one to three autos before backing out. In fights, press it when targets are already entering your range, not while you are still walking for access. A bad W is rarely one that deals zero damage; it is one that starts a long exchange you cannot finish safely after the range window closes. If you are unsure, wait one beat longer and make sure the timer will be spent shooting, not repositioning.
4 seconds after dying, Kogmaw explodes, dealing true damage to surrounding enemies.
Kog'Maw launches a corrosive projectile which deals magic damage and corrodes the target's armor and magic resist for a short time. Kog'Maw also gains additional attack speed.
Kog'Maw's attacks gain range and deal a percent of the target's maximum health as magic damage %i:OnHit% On-Hit.
Kog'Maw launches a peculiar ooze which damages all enemies it passes through and leaves a trail which slows enemies who stand on it.
Kog'Maw fires an artillery shell at a great distance dealing magic damage (increased significantly on low health enemies) and revealing non-stealthed targets. Additionally, multiple Living Artilleries in a short period of time cause them to cost additional Mana.