Marks:
Magic Penetration


Seals:
Armor


Glyphs:
Magic Resistance per level


Quintessences:
Armor

This section is simple. Amumu benefits most from all items in the Defensive Tree Masteries. We want Amumu to be as tanky as possible, and this is where Amumu will benefit the most early game.

In non-ranked games:



In ranked games:

I personally like Boots of Swiftness They are useful for keeping up with a fleeing enemy, or getting our of hairy situations. However, if the opposing team is mostly made up of physical damage champions I will use the Ninja Tabi Ninja Tabi size


The problem we come across in most ranked games is the amount of Crowd Control effects that are used. This requires more anti-CC items which is when Mercury's Treads become a must

Situational items:

Amumu is all about Area of Effect (AOE) abilities and getting into the middle of things. To increase the synergy of his AOE abilities, every item is meant to up his armor, magic resistance along with an AOE item.

Philosopher's Stone
The first thing we want to do with Amumu is increase his gold income while enhancing his laning sustainability. We get all of it with the Philosopher's Stone.


Sun Fire Cape becomes an item that is essential. This is an item that I prefer to get earlier rather than later whenever I am in solo lane or in the jungle. This increases health, armor (much more important in the jungle than magic resistance), and gives an AOE effect that really ups the damage outage coming from Amumu to allow easier and quicker farming/jungling.

The only time I do not get this item first is when I am not solo laning or jungling.
When in duo lane, I rush Aegis of the Legion .
WHY?
Because the main reason I get Sun Fire Cape Sunfire Cape size is to farm more effectively, but with a laning partner, my priority is to allow them to get as much gold as they can. My first priority then changes to support, which is why I rush Aegis of the Legion . With Aegis of the Legion rushed quickly in duo lane, you will likely win lane fairly easily because your laning partner will be able to be much more aggressive.


Force of Nature is the main magic resistance item I prefer to take with Amumu due this item providing more Magic Resistance than any other item in the game. Let us not forget, the increased movement speed and health regeneration is nothing shabby either.


Guardian Angel is an excellent item for champions with tons of armor and magic resistance.

REASONING:

No matter what you get 750 health (no more/no less) restored to you when you die and Guardian Angel brings you back to life. However, 750 health is much more difficult for enemies to eat through if you have 300+ Armor and 250+ Magic resistance. Since this Amumu build is focused on Armor and Magic resistance, Guardian Angel is a core item in this Amumu build.


For this Amumu build, I choose Frozen Heart over thornmail for 4 reasons:

1. Amumu gets additional mana from Frozen Heart which is greatly needed .
2. Amumu gets a much needed cool down reduction from Frozen Heart .
3. The slow effect is great for against On-Hit-Effect/DPS enemy champions due to the reduced attack speed it causes.
4. I do not want to encourage the enemy team to focus my teamates. I'm tank, therefore, I should be initiating and soaking up the most damage during ALL teamfights.

Banshee's Veil is the item that most often well be selected especially in ranked games where having another anti-CC item is worth every cent you pay. It gives extra health, some excellent Magic Resistance, and the invincibility bubble that you get every 45 seconds is unmatched.


If the other team has much more physical damage then I will consider Randuin's Omen . This will usually be the case when the other team has 3 physical damage carries, one tank and only one magic damage carry. Other than that I go with either Aegis of the Legion or Banshee's Veil


As mentioned above when explaining Sun Fire Cape Sun Fire Cape, I get Aegis of the Legion when in lane with another champion which helps win lane and becomes an excellent support item for team fights in later game situations.