Cube all 3 organ (Baal's Eye, Diablo's Horn, Mephisto's Brain) in Hell Act 5 to create a Red Portal to Uber Tristram where you'll fight 3 Uber Bosses at once for the Hellfire Torch.
Be prepared. This is really difficult.
1* Baal's Eye
1* Diablo's Horn
1* Mephisto's Brain