Hello there all LOL players and GARNUZ, hehe if you've played with him you would know why I said that...(j/k he's a nice rl budd)
Okay but now we gotta get serious >:|, I've made this guide to pay back all that moba and those guide writers have helped me out in my gaming, this is my first guide too soooooooooooooooo bear with me please.
As you see most of the amumu's build guides out there are great! However this guild is based on an amumu that can tank and as well making hell lot of damage.
Trust me by end game if you follow this build would have over 3.8k hp and over 200 ap, with enough defense and mr to still be a tank, so dont be afraid to 1vs1 anyone!

Pros:
He is an awesome initiator
Deals a real good AoE amount of damage
His ulti can really turn the other way teamfights (you know in your favor)
Good ganker (you know...if you can hit your bandage toss)
Good farmer
Free hugs


Cons:
Squishy early game
You really need to hit his bandage toss if you wanna get the best out of him
He is kinda emo.

I will start out with the jungle route.

Either if you are starting with the 18 armor item and 5 Health Potion
Or wanna rush to philosopher's stone starting with Regrowth Pendant The jungle route is the same but if you are rushing to philosopher's tell your teammates to give you a decent leash.You wanna start out on the blue golem, ask your team to give you a leash. (means the mid or top lanes champion hit him once or twice and then leaves). After the leash turn on your Despair and start headbutting that golem's butt! and once he is low enough Smite the heck outta him! You will use your first Health Potion here.

Wolves is station number 2! and now you should be lvl 2 too! woo isn't that awesome?! Okay turn on your Despair, use your Tantrum keep hitting the big brown wolf, WIN! you might wanna use your 2nd Health Potion here, while you are fighting or while heading to wraiths.

Wraiths! 3rd station, turn on your Despair and Tantrum those f******! hit blue wraith twice then hit once each of the other wraiths, Tantrum again! win!

4th station is golems! by now you should still have 3 Health Potion, repeat the skill sequences and Win! Grats you are lvl 3! You might have to use your 3rd Health Potion pot while fighting here.

5th station is the red lizard, okay now turn on your Despair then Tantrum him! Bandage Toss! Tantrum again! Smite! win! Now you should have 2 Health Potion by now use them if necessary.

As you see I placed little yellow triangles with ! point in them, careful this places you might get counterjungle so be sure to always have enough hp to get away (remember you have 5 hp pots!)

You will noticed I marked some really ugly lines in the lanes, well if the enemy passed the golden line its heads up! go there and wrapped yourself in for a gank! Be sure you tell your team members what are you gonna do. Behind the green line is still good, but they need to have kinda half hp. Behind the red line is dangerous dont go unless they got little hp and you and your team mates will kill easily. Yellow dots indicate where you wanna place yourself for the ganks.

As a jungler your work is to aid your team mates in trouble, hold lanes and gank.

Smite is a must for this jungle amumu it makes your jungling way faster and also gives you a nice gold bonues everytime you use it. I set up my smite in D but you set it however you feel more comfortable.
Flash ahh... what a great spell, useful to run, to chase, to position yourself during teamfightings wich is really important since you want to wrap up as many enemies possible with your ultimate. I set up my flash in F since I like it that way, you set it up as you feel like it.
Another really useful spell is Teleport since you will be doing a tanking job you really wanna get to teamfights as fast as possible, or help out someone who needs help.
Ghost is a good spell to but not very viable with this build, you wont be chasing people as amumu so...I dont really think is a good spell
Fire you got enough damage already dont need more. Is more of a lane mumu spell

That build on top is really solid, Ad carriers wont like to attack you because of the thornmail, and you have pretty decent MR, and tons of damage over time.
However you might like to alter the order in wich you buy your items, or change one or two of them.
E.G:As you can see the other team is Ap heavy, Gangplank makes ton of damage but again he is really squishy early-mid game,and Talon...well he wasn't good so I didn't need to worry about him... As I was saying you wanna rush your Force of Nature. But they got Veigar dude! why would you want MR!?, the fact is that veigar is really squishy and if you can position yourself right and Bandage Toss him, Despair, Tantrum, Curse of the Sad Mummy and hes pretty much dead, and it was easier since there was a good Malphite in our team.
You can see I traded here Rod of Ages for an Abyssal Mask, Why I did that? well again with the MR combined of Force of Nature and Abyssal Mask the other team wont bother much on casting their spells on you, it gives you some really nice ap and their aura ability is just perfect for you!.

In case the other team was Ad heavy you wanna rush your Thornmail as fast as you can after getting of course a Giant's Belt since it doesnt work out pretty well when you have 1.2k hp...
Well you see the result...your end game would be pretty devastating, notice how I had more gold than Gangplank even he had more kills and 1 less assist? Philosopher's Stone thats right you really wanna hold on to this untill you get your last item.
Heres another example of a final build, again the other team was really ap heavy...oh and theres my friend garnuz Twitch lol 64 creeps at 45 min game...he is such a troll xD...

You are an offtank, once you hit lvl 6 if someone is poking you with its damn autoattacks dont be afraid to face them. Bandage Toss, turn on your Despair, Tantrum, keep following them around and headbutting, if you think you can kill them Curse of the Sad Mummy, Tantrum again and try pulling that last Bandage Toss.

Since this game is all about team fighting I'll explain you your role here.
As an offtank you are the initiator of the fights, means you gotta go in there do as much damage as possible, keep your carriers alive (harrass those people attacking them) and dont be afraid to die if you manage to make your team get 5 kills and only 1 death.
Iniating with amumu is pretty simple you have to Bandage Toss someone, turn on your Despair, Tantrum and keep tossing your Bandage Toss and using your Tantrum

Curse of the Sad Mummy Thats what you gonna have to time, usually after the first Tantrum you might wanna use it, but that is up to you.

Another thing is learn when to start out a fight, if all your team it's pretty much dead or your Ap people without mana you shouldn't start, if you Bandage Toss in they will just let you die...and it's not their fault.

Heres a Printscreen of me and my results, feel free to post yours around.

At last thanks everyone for reading my guide, feel free to make any suggestions that might make this a better guide. I'll keep working on this guide to keep making it more in depth, its not quite finished yet!

I didn't made the image on top, credits goes to this guy http://he-st.deviantart.com/