Planescape Torment:
Outlands
You come here from the Curst Underground. There are tons of monsters - run west and south. The grillig and gronks will attack, but the trichast and lim-lims won't. Go into the skull of the skeleton. Thisis the home of Fjull the Forked-Tongued Fiend. He's required to help you out. He doesn't like Tanar'ri though. He says your mortality is in the Fortress of Regrets. For 350,000xp he says on Baator, a pillar of skulls knows where this is. Morte doesn't want to go there.
The skeleton is of Ul-Goris. He says the portal to get to the pillar is under the arm of the skeleton. Before you go, ask how you can return!! For 100,000 he'll explain that you need a jagged piece of obsidian to open the portal.
When you return again, don't take what the Fiend offers you, it's what he needs to survive. You can now go back to Curst through a new portal in the skeleton's tail. However, when you return, you return to a Destroyed Curst - "Curst Gone".
Planescape Torment Walkthrough
Walkthrough Master Index