The first thing you write in this guide is: "Ok first of all, you've gotta except the fact your the tank and not the carry :(" and when I see your masteries and items I just thought that you don't know what you were doing or talking about. I'm talking about the ~3000gold wasted on frozen mallet and the mastery "ardor". Warmogs would be much, much better than mallet on amumu and "defensive mastery" instead of ardor would atleast not be wasted points. When you attack/harass ppl early game you get the agro from creeps and taking less damage from them is ofc better. The positive I can say about this guide is probably only the Item Core 1/2/3 is somewhat better then the "displaying" one. Don't like your runes either.

Amumu is my main char, played atleast 2-300 games with him. No team is like another team, you always have to build tanks after the opponents team damage output. Just need some remaking so start thinking. For example, build for 2x carries(phys dps) and 2x casters or maybe 1x carry, 3x casters and so on.

Regards