Playing Kog'maw is fairly simple, first you farm off of minions then you go for the kills. You want to buy a dagger early game, to ensure your killing of minions, which you then turn into a Madreds. The core of his damage mainly comes from his Bio-Arcane Barrage(w) and the Madreds Bloodrazor because of the bonus percent damage. Berserker's Greaves gives Kog'Maw a little more attack speed and movement to help him with the basics. The Malady and the Wit's End also contribute greatly because of the On-Hit damage and attack speed. The Bloodthirster is for the life steal and some AD to help aid you on your journey. With the lifesteal, Kog'Maw can last in battle for a long time. Lastly the Frozen Mallet is in the build to help chase down enemy champions with more than just his ultimate. With the complete build there will be massive amounts of bonus damage.