So, here's a guide to Amumu that I've recently started using regularly. It works in almost any situation, but be warned, it's very possible to get kills with this/not die ;) My first game with this build I went 14/1/18. You can tank and do damage! Wow! I mean... LOL!

This build is great for a team, because depending on the strength of your teammates you can end up carrying your team, or just as a really great support. This build really pulls the team together no matter which role you end up with. :)

Start off with the Heart of Gold. This helps you gain money faster through out the game, and gives you a great start having more health than most other champs. I then typically get boots, then a giants belt to help with the tank factor, but the rest of the items can be subbed in any order really depending on how the game is going and what you need. For example if you're getting nuked by a Veigar, you'll probably want to build magic resist quicker.

Just start with bandage toss, then level up in this order: R, E, W, Q.

Depends on preference. I use teleport and ignite. Teleport helps you get into the action way faster, and ignite helps you finish it off.

Heal can be good, especially in a lane against two AD carries :P

Smite... Wanna jungle this? Give it a go. Super fun! XD Amumu coming out of the bushes is one of the (cutest) but scariest things ever with his double stun.

There you have it. Best of luck!!! And most of all, have fun! :)