DEBUFF, debuff and (guess what) more debuff!

This guy have so many skills that I will never be able to use all of them in one battle!
Also, even if you are not that kind that use those darn actives, you will still have a decent offtank, health, armor, magic, and some of ur items have some passive effects to.
Wanna go pro? Time for an all active build! :D

Ok, now a little talking about how to play with this guy, so that i write over 5000 characters:

Start with building a bit of a flesh on you, since Amumu lack that pretty hard at start. Get a ruby. Farm, use E when needed to get a last hit, might be easyier if you can jungle, anyway, just try to get da money for the next step asap: upgrade ruby to HoG and get socks the next time you visit town.
Now we have a bit of a flesh on us, time to c that it stay so, it's time to get regrowth pendant, or if we did good and have da money, buy philosopher's stone directly. Don't forget to upgrade the boots to, mercury's are the usual boots for Amumu, but depending on circumstances, Ninja Tabi or Sorc Boots may be better.
Third now, get some ap and that's also another item that give u free cash: Kage's Lucky Pick.

This was early to mid. game, now you should know what you are facing, and things have to be adapted to that. Need armor? Get chain mail, upgrade it to warden asap. Need ressitance? Get Odin's (or Banshee's) Veil. Need a watchfull eye? Get Hextech Sweeper. Sorry guys, I played so much Dominion lately, that I see only Dominion items everywhere. In normal games, get the Will of the Ancients if you will, and wards for the part with invisible foes. Or you don't need any of them, and can build more power? Get the Fiendish Codex.

And, the later game, time now to complete your build.

P.S. Have fun!

Hmm, still not 5000 characters, so I will have to fill more of this space, and of your time.
Way to attack? Think that you and other jumpers stay in a bush near a lane. Pull urself (with Q) to an enemy (think there are 2 or more there?) and start crying the same time, cast Deathfire Grasp on the tankiest guy, cast E when you are near them and, if it worth it, R. Then we have a little brawling there, if they fight back you check Odin's Veil and pop it, again if it worth. In the moment you see them trying to run (or your friends running), use Randuin's Omen, and if things are not clear after that, use Shurelya's Reverie to. Either way it's going, you may still be breathing, and your enemyes will number their deads.

Active skills? Hip Hip Hurray!