Bul-Kathos' Nightmare

Bul-Kathos' Nightmare is one of the five summon materials that open the Colossal Summit, where you fight the Colossal Ancients. In Hell, the act bosses drop summon materials, and these bosses drop Bul-Kathos' Nightmare as theirs:

• Diablo: 90% of the time
• Mephisto: 5% of the time
• Baal: 5% of the time

Transmute one of each in the Horadric Cube in Harrogath, in Hell, to open the portal:

• Talic's Anguish
• Korlic's Pain
• Madawc's Ire
• Bul-Kathos' Nightmare
• Worusk's End