Mustrum_Ridcully
Legend
The Abyss gets its own chapter "Into the Abyss"
There is less about its origin and more about its nature there.
Interesting concept: The Worldship, a giant stone spelljammer, crewed by dwarves, genasi and a few tieflings, is exploring the abyss, trying to reach the center of the pit. A deva aboard continually reincarnates...
The chapter suggests two campaign arcs, one for paragon and one for epic tier. A sidebar notes that the Abyss is not a good place for heroic characters, even though they might sometimes stumble into it (or more likely into something coming from it), it's not a place to stay and explore for long...
There are some skill challenge suggestions.
o Abyssal Madness is about not going insane while staying in the abyss. Whenever you fail a check as part of the challenge, you suffer an insanity effect. Failing the challenge means they stay, everyone gets an extra insanity and a remove affliction ritual is required. Doesn't sound so bad, insanities are fun, right?
Well, you sure will like "Paranoid Delusions", turning you into an non-ally for everyone or Melancholy that takes away one of your actions... 
o Destroying A Demongate. Well, self explanatory. Failure or Success, it will hurt the party.
o Escaping the Demon Horde. When there are just too many of them. If you fail, you face a tough encounter and have to try again.
o Navigating the Demoweb. Don't get lost.
Abyssal Locations
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o Mal Arundak, Bastion of Confusion. Something is imprisoned here. It is believed to be Tharizdan, at least that's what the gods told the angels guarding it.
o Molor, the Stinking Realm. Jubilex,patron of slimes and oozes, rules this place. It's not his domain, but if he does't take care with Zuggtomy, it might become it.
o The Plains of Rust. A place that used to be a stronghold for Devils thanks to 3 portals leading to Hell, but was wrecked by Orcus and Jubilex.
o The Spire of Rajzak. Razjak is a gargantuan creature, terribly bestial but as powerful as a demon lord. It is said that was he was before Gra'zt destroyed his soul and mind.
[/sblock]
There is less about its origin and more about its nature there.
Interesting concept: The Worldship, a giant stone spelljammer, crewed by dwarves, genasi and a few tieflings, is exploring the abyss, trying to reach the center of the pit. A deva aboard continually reincarnates...
The chapter suggests two campaign arcs, one for paragon and one for epic tier. A sidebar notes that the Abyss is not a good place for heroic characters, even though they might sometimes stumble into it (or more likely into something coming from it), it's not a place to stay and explore for long...
There are some skill challenge suggestions.
o Abyssal Madness is about not going insane while staying in the abyss. Whenever you fail a check as part of the challenge, you suffer an insanity effect. Failing the challenge means they stay, everyone gets an extra insanity and a remove affliction ritual is required. Doesn't sound so bad, insanities are fun, right?


o Destroying A Demongate. Well, self explanatory. Failure or Success, it will hurt the party.
o Escaping the Demon Horde. When there are just too many of them. If you fail, you face a tough encounter and have to try again.
o Navigating the Demoweb. Don't get lost.
Abyssal Locations
[sblock]
o Mal Arundak, Bastion of Confusion. Something is imprisoned here. It is believed to be Tharizdan, at least that's what the gods told the angels guarding it.
o Molor, the Stinking Realm. Jubilex,patron of slimes and oozes, rules this place. It's not his domain, but if he does't take care with Zuggtomy, it might become it.
o The Plains of Rust. A place that used to be a stronghold for Devils thanks to 3 portals leading to Hell, but was wrecked by Orcus and Jubilex.
o The Spire of Rajzak. Razjak is a gargantuan creature, terribly bestial but as powerful as a demon lord. It is said that was he was before Gra'zt destroyed his soul and mind.
[/sblock]