Abilities of Kog'Maw
Spell skill priority is an important winning factor for Kog'Maw. Understanding the abilities of Kog'Maw in League of Legends is another. Below you can find all the relevant information on Kog'Maw abilities. In order for item builds you should check the build for Kog'Maw.
Passive: Icathian Surprise
4 seconds after dying, Kogmaw explodes, dealing true damage to surrounding enemies.
Caustic Spittle
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.
Passive: Kog'Maw gains e2% Attack Speed.
Active: Kog'Maw vomits a corrosive projectile that deals totaldamage magic damage to the first enemy hit and shreds shredamount% Armor and Magic Resist for e4 seconds.
Bio-Arcane Barrage
Kog'Maw's attacks gain range and deal a percent of the target's maximum health as magic damage.
Kog'Maw gains e1 Attack Range and his Attacks deal an additional totalhealthdamage max Health magic damage for e3 seconds.
Void Ooze
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 spits bile, dealing totaldamage magic damage and leaving a trail of ooze for e3 seconds. Enemies in the ooze are Slowed by slowamount%.
Living Artillery
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.
Kog'Maw shoots acid at an area, dealing basedamagecalc plus tooltipmissinghealthdamageamp% per 1% missing Health magic damage and revealing enemies hit for 2 seconds. Enemies below 40% Health instead take maxdamagecalc magic damage.
Subsequent shots within manacostduration seconds cost an additional basecost Mana (max: manacostcap Mana).
FAQ on Kog'Maw
What do you max first on Kog'Maw?
Most Kog'Maw pros max out 
Void Ooze first.