Not Updated For Current Season
Alright, this is my first build and I owe a lot of credit to several builds/guides that I've read and used as well as trial and error.
First off, I can't promise kills with this build, most of my games I end up coming out with something like a 9/7/26. I have found that playing Amumu I am generally ending up with a good bit of assists and usually become the initiator or finisher in a big team battle using Curse Of The Sad Mummy at the proper time and with proper back-up from my team.
Alright, starting off in a game I grab the Regrowth Pendant and head into my lane with my partner. As far as early game techniques, I usually play a happy medium of harassment / focus on last hitting, all depends on how confident I am in my opponent as well as my partner. Skill wise, I start off with Tantrum because I focus on farming to get my Philosopher's Stone, although its cost is very little I still find my play style fits best this way.
Still farming and being careful of your lane push as to not draw so much attention to possibly be ganked, I will usually be sitting happy with my Philosopher's Stone and be making my way towards either Ninja Tabi or Mercury Treads based on the majority of my enemies being either melee or more on the magic/caster side. In most cases, I will get Tabi.
I suppose mid-game is soon coming up and most if not all champs are rocking their Ultimates and are doing noticeable damage. This is wear I really like the idea of having my Banshee's Veil. You have 450 Health, 400 Mana, 57 Magic Resist and of course the negative spell block every 30 seconds. I just find it nice to have at this point in game, and in long-term play.
As I said this is my first guide so I'm just trying to cover things the best I can. Now, continuing. It's mid-late game and I am going for a Thornmail. The 100 armor isn't bad at all, and the 30% return on standard attacks never hurt anybody, nice for farming as well as big team battles where if you're in any way like me, I'm sitting repeatedly click on an enemy as well as smashing buttons waiting on cooldowns.
Hopefully you and your team are doing well and able to work together as a team during these big battles that are undoubtedly going to happen, I may be going off track item wise, but I want to touch base on somethings, hopefully farming is and has been going well, hopefully your team hasn't fed anyone, and things are looking in your favor. In the big battles that take place or the ganks that are being pinged on map, I love opening by tossing my bandage, bringing on the tears, and hitting the Curse Of The Sad Mummy, followed by smashing Tantrum =] Usually works out for the best of course, when you aren't doing all this alone, and you have a helpful group of friends there to take the killing blow when and or while your Curse is going off, makes things much easier.
Alright back to items, at this point its near end game, you and or they are pushing your inhibs, and things might be stressful, who knows. I'm aiming for my Sunfire Cape at this point if I don't already have it. Now, that makes you a decent threat as far as being anywhere near you, whether being a minion or champ, you're not untouchable, but you can def cause some health to drop along with your Thornmail.
To finish things off I'll usually stack another Sunfire Cape, then I'll usually sell my Philosopher's Stone, save up and get a Force of Nature depending on the enemy, or go 1 Sunfire Cape and top off with Lich Bane.
Anyway, all in all this is how I have been playing, and at times items are different, but the large majority of my games end up with this type of setup. I'm in no way a pro, and I'm always learning new things, how to do this or that, adjusting play style vs different champs, etc. The game is forever changing most of the time and their are plenty of ways to play all the champs, hence all the guides on this site. Thanks for your time reading my guide, and please if negative comments or suggestions are made, explain why so I can not only take into consideration but try out for myself as well.