Diablo's Horn

Diablo's Horn is an item needed in the Pandemonium Event. It is one of the 3 major keys represented by body parts of the Prime Evils, the other two being Mephisto's Brain and Baal's Eye. The horn can be acquired by defeating Lilith in the Matron's Den.

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