As Amumu you are going to be in and out of the jungle constantly ganking a lane, this is the reason for the Attack Damage. The extra 5 gold from the 2 items will help alot because when you are going from lane to lane you will get gold and it will make up for some of the gold ur not getting from the jungle. I suggest getting Red buff as much as possible! The 5 health pots will help early game when going from lane to lane and in the jungle as well.

Teamwork meaning communication is going to be very important as a jungler. Knowing when to gank a lane will help A LOT! when trying to take a buff or golems.

Pros -
Good Jungler

Cons -
Kind of squishy early game

I get Marks of Strenght for Amumu just because its more Attack Damage early game to take buffs and golems a little faster, it will also help early game if a gank is needed. The Seals will help in both the jungle and the lane early game. Glyph of Warding gives that Magic Resist you will most likely need. I also decided to put the health Quintesences in this build for the extra health throughout the game.

The masteries for this Amumu build may be set up a little different than most but I believe if you take a look at them, you will come to see they will help you. Picking up as much gold, cool down reduction, damage, exp. will help you going from lane to lane.

The Items in my Amumu build are pretty much the same as most jungle builds.

In this part of the build, it as pretty much the same as my item description, its pretty much the same thing.

My summoner spells are Smite for the taking of Dragon and Baron Nasher. Flash is to get away from trouble in the lane and maybe used to get to a quick buff steal.

You probably wont get as much of a minion farm since you are in the jungle but when leaving a lane after a successful gank I advise you get as many minions as you can that are in the wave/around you at the time and go back to the jungle, recall for an item or 2, or go for another gank.