Okay, are you ready for a bunch of criticism? I won't downvote because I don't think this guide is bad, it just needs some work. And maybe some correction.

As Amumu you should usually be shooting for 0/16/14 or 1/16/13 masteries. The utility tree is very much superior for junglers, especially for tanky ones that don't need the offensive tree. Archaic Knowledge is NOT worth it on jungle Amumu, while Awareness and Utility Mastery are HUGE for jungling.

Strength of Spirit is one of the most powerful masteries in the game, even if you don't get any bonus mana. Since dodge doesn't work as well with Amumu, it's a great alternative to get down the defensive tree.

Abyssal Mask doesn't stack well either. Seriously, you should avoid stacking items (other than doran's blade or ring) as much as possible. Every time you double up an item with a unique passive, you are wasting a boatload of stats. Get Banshee's Veil if you really need more MR.

Aegis of the Legion is an amazing item on Amumu. Even if you don't put it in your core build, it at least deserves an honourable mention. While you're at it, your guide could do with some situational items. It's good to know which items to get based on team comp, especially for a tank.

I agree with Keels when he says that Ninja Tabi are BAAAD on Amumu, especially jungle Amumu. It will slow down your Tantrum CD every time an enemy attack misses. You're better off with Mercury's Treads. Ninja Tabi are situational boots at best (unless you're Jax), so since there's a downside to using them on Amumu, they're usually a bad choice.

You're wrong about gold/10 items. They're technically the most cost-efficient items in the game, and are used in pretty much all high-level and professional games. I'm not saying they're essential for this build, but don't underestimate them. Get Heart of Gold if you ever build Randuin's Omen, and Philosopher's Stone is a great way to recover from counter-jungling, especially if you've lost your blue buff.

I'm a fan of Greater Glyph of Scaling Magic Resist on junglers, especially jungling tanks. Greater Glyph of Scaling Cooldown Reduction is okay, but you don't really need them for Tantrum and Despair, so they're less effective on Amumu than they are on other champions.

I'm liking the coding, but your guide could use some larger icons too, maybe to head each section. An image of your jungle route for quick reference would be great as well.

I think Fortify and Teleport are situational spells. Ghost and Flash are far superior, but you may need a tele or fortify on your team to prevent pushes. I wouldn't say to recommend them, but listing them as possibilities (less viable than ghost/flash) would be nice. Cleanse is also important for some players, so you may want to give that spell a little more credit.

You say you get Sunfire Aegis first (a fine choice) in order to solo dragon. While it's nice to have this ability, in high level games you should almost never solo dragon. It's always safer, faster and better to have 1-3 team mates come help you.

• An image of your jungle route.
• Some changes based on the suggestions you've been given, or at least a response.
• Pretty pictures and icons. Even with the coding you have, it still is a bit bland.
• Situational items
• Tips and tricks on how to use abilities. You have some already for escape methods, but it's good to know how to use his abilities offensive too. Don't assume your reader knows everything about Amumu already.
• An abilities section explaining the importance and function of each ability, including the passive. See my Nocturne guide or Jhoijhoi's Guide on Making a Guide for some formatting if you like.
• A team fight section. Explain Amumu's role in a team (don't just say, "tank") and how to perform before, amidst and after a team fight.
• A conclusion, maybe with credit to suggestions from readers, inspiration from other guide makers, or a simple farewell and good luck. Your guide ends rather abruptly.

That's all I've got for now (sorry about the wall of text). I look forward to hearing from you.

EDIT: Nice title by the way. I chuckled.

I edited (added) the items section to address your comment. As for the 9 - 21 - 0 part I don't know what that is supposed to mean. In a recent game of mine I dealt 350 thousand damage as Amumu given that the game was 55 minutes. So I think even if the passives don't stack the base stats stack very nicely.

No. A) FON doesn't stack. B) Ninja tabi messes with your Tantrum]. In other words, never get them on amumu, especially if you're jungling. C) 9-21-0 is bad for jungling amumu. I suggest you hit level 30 before posting on mobafire.