i always get the question: "why are you going ap with amumu? he is a tank!" its true, he is a tank, but hes also an amazing dps and farmer/pusher with ap, cuz his bandage toss and curse of the sad mummy gets 100% power out of his ability power, witch means his ulti if he get 400ap, it will deal 750 in a large aoe plus stun, and with his bandage toss, he can deal 1400 dmg +++ to one champion in less than a secound.
Tantrum is a nice aoe farming spell, as well for harassing and dmg, with tantrum he can remove whole lanes in matter of secounds and its nice for foresting as well
Despair get more dmg as well, and help on farming as it does not cost much mana at all, and is nice dmg if u activate if before using bandage toss on an enemy, then followed by tantrum and ulti. this combo can turn around a whole teambattle easly, even if opponent is more feeded than your team.
This build requires alot more skills than if going tank build, you have to be more accurate with bandage toss and have to do things more accurate to get most out of ur abilities in fights cuz your alot more squishier with this build than with a tank build.
This build is working better 3v3 than 5v5.