Amumu Runes explained
There's one set of runes for Amumu on patch
11.21
that is the clear favorite for LoL players and pros alike. The best Amumu Runes on the position 
Support are Resolve as the primary path and
Domination as the secondary path with a pick rate of 58%. Besides runes you should take a look on Amumu Build and if you are interested in pro matches take a look at Amumu Probuilds. If you want to discuss
Amumu then you should visit the champion subreddit.
Primary path on Amumu
Resolve empowers the survivability of Amumu and increases the tankiness. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Aftershock is the best keystone rune to run on
Amumu. This keystone rune bulks you up, increasing both armour and magic resistance, once you immobilized a champion.
Aftershock synergises both with the sheer amount of crowd control Amumu possesses and the need to be tanky as soon as you engage. This is usually followed up by taking
Font of Life,
Bone Plating and
Unflinching.
Font of Life provides your teammates with more sustain by healing them whenever they attack a champion whose movement you've recently impaired.
Bone Plating make Amumu overall tankier, by decreasing the amount of poke damage in the early game.
Unflinching inceases Amumu tenacity based on your missing health.
Secondary path on Amumu
When it comes to your secondary path, most
Amumu players prefer to go with
Domination.
Domination improves burst damage and assassination tools on Amumu. On the
Domination path, the best runes for Amumu are
Ultimate Hunter and
Cheap Shot.
Ultimate Hunter scales up Amumu ultimate haste on every unique champion takedown.
Cheap Shot makes you deal more damage to enemies with impaired movement, which has great synergy with the setup of Amumu.
FAQ for Amumu Runes
Which is the best keystone rune on Amumu?
The best keystone rune on Amumu is
Aftershock.