Kog'Maw Runes explained
There's one set of runes for Kog'Maw on patch 15.12 that is the clear favorite for LoL players and pros alike. The best Kog'Maw rune paths on the position 
Adc are 
Precision as the primary path and 
Resolve as the secondary path with a pick rate of 58%. Besides picking runes on Kog'Maw you should learn how to play Kog'Maw and if you are interested in pro matches take a look on how a pro builds Kog'Maw. If you want to discuss 
Kog'Maw then you should visit the champion subreddit.
Kog'Maw runes from primary path
Precision improves attack and sustained damage on Kog'Maw troughout the match. Most of high elo players – and our LoL pros in the the major regions – have agreed that 
Lethal Tempo is the best keystone rune to run on Kog'Maw. This keystone rune gives Kog'Maw a great head start in team fights and allows to put out more damage in that time window. Other primary runes on Kog'Maw are 
Presence of Mind, 
Legend: Alacrity and 
Cut Down.
Presence of Mind helps Kog'Maw with the mana problems by restoring missing mana, if a champion is killed. Legend: Alacrity grants additional attack speed to Kog'Maw. If the enemy team consists of multiple tanks, then the rune Cut Down is the best choice.
Kog'Maw runes from secondary path
When it comes to your secondary path, most Kog'Maw players prefer to go with Resolve. Resolve empowers the survivability of Kog'Maw and increases the tankiness. On the Resolve path, the best runes for KogMaw are 
Overgrowth and 
Conditioning.
Overgrowth increases your maximum amount of health. Conditioning powers up Kog'Maw tankiness after the laning phase.
FAQ for Kog'Maw Runes
Which is the best keystone rune on Kog'Maw?
The best keystone rune on Kog'Maw is Lethal Tempo. This Kog'Maw runes setup is then referred as Kog'Maw Lethal Tempo.
What runes does Kog'Maw use?
Runes from the paths Precision and Resolve are the most used runes on Kog'Maw. For the exact pick rates of Kog'Maw runes used, you have to study the rune distribution presented.