Amumu

the Sad Mummy

Tank

Solitude can be lonelier than death.

The build that broke the game

Sorcerer's Shoes

Sunfire Cape

Abyssal Scepter

Rylai's Crystal Scepter

Spirit Visage

Randuin's Omen

Why it worked

Curse of the Sad Mummy stunned a whole team in one go, with no cast time and nothing to react to. Despair burned percentage maximum health while Abyssal Scepter removed exactly the magic resist that would have blunted it. With Sunfire and Rylai's, standing anywhere near him was already a losing trade.