Mephisto's Brain

Mephisto's Brain is an item needed in the Pandemonium Event. It is one of the three major keys represented by body parts of the Prime Evils, the other two being Diablo's Horn and Baal's Eye.

Putting the Brain along with the Horn and the Eye in the Horadric Cube in Harrogath on difficulty opens a portal leading you to Uber Tristram where the ultimate challenge awaits...