Author's Notes: Here is a Planescape adventure I ran quite some time back. If you wish to use any/all of it, feel free. Let's just clear a few things up first.
That's all there is for now. Here's the adventure- it's a bit on the disjointed side, cause that's just how I am, but hopefully you'll be able to put it together nicely. My own notes from the time I ran it are at the end.
Plot Outline: The characters awaken on a mobile baatezu fortress, with no idea how they arrived there. The baatezu have allegedly magical contracts stating that the heroes will participate in this mission in return for a payment. The contracts are designed to slowly kill anyone who breaks them. The heroes have allegedly signed them. Their last memory is being asked to visit a house in Sigil. They must
Player Text:
"You are awakened with a splash of water on your face. One by one, a large ugly and metallic looking face, with a bulbous nose and scales jutting out at all angles, looks you over. It's bottom fangs peek through as it smiles, then stands to its full 9-foot height and shouts something behind it.
"The room is very dim, lit only by a few low candles, and it only has to take three steps back to get out of sight. At that point, it's place is taken by an even more fearsome creature. A fearsome 12-feet tall, this creature is a deep blood red. It's huge bat-like wings wrap around it's entire body save the head, from which two glowing white eyes peek at you. It flashes a toothy grin. It could only be a Pit Fiend. 'It iss good that you have ssurvived. You are... intact, I trusst?'
"You are in a small amount of pain, but it is more the kind of pain
that lingers for a while after injuries are healed."
(No matter what the party says, the Pit Fiend asks, "How much do you
remember?")
After saying they don't remember, "Sssuch weak minds, you mortalsss sseem to have. The water from the River Ssstyx took your mosst resssent memoriess. It is quite potent here..." He pauses, then looks back, presumably at the creature that awakened you. "Grul. Brief thessse men. Again. I have more important matterss to attend to." In a flash of green light, the Pit Fiend vanishes, leaving only a wisp of dark smoke.
Grul, the cornugon steps forward. "You are aboard the Leviathan, one of our mobile citadels. We are currently in Gehenna, nearing a large portal to the Grey Waste. From there, we will pass through Carceri and locate a secret portal in the Abyss." He spits as he says Abyss. "Our destination lies there."
Possible Questions from the party:
- Where do we come in?
"Three days ago, you signed on for this mission with us in return for
some monetary compensation. Surviving members of your group are to be
paid at the conclusion of the mission."
- What is the mission?
"We have learned of a layer of the Abyss (spits) where very few of
the mindless tanar'ri exist. It is hospitable, barely, but there is only
one known entrance. Our duty is to break through the bottleneck, and
establish a foothold there to launch our armies. Projected casualties
are high, but we have a good chance of success."
- We won't go through with the mission/What proof do we have we agreed?
"There is a phrase among you mortals. The only thing more deadly than
making a contract with a baatezu is breaking a contract with a baatezu. At
the beginning of this journey, you signed a contract. The contract is
designed so that if one side breaks their signed word, they will wither and
die within hours. I'm told it is... quite painful."
- What is our role in the mission?
"You will have many varied uses. First and foremost, you are going to
open some of the portals in the Abyss. Many are designed so that a
baatezu cannot activate them. However, if a mortal activates them, nothing
stops us from making use of it. Secondly, you may be called upon to scout
out enemy positions. Finally, as weak as your mortal bodies are, you will
fight in any battles. Basically, we may ask you to do anything that comes
up that we cannot, or we do not wish to risk our forces on. The contract
binds you to follow the orders of the Leviathan's commander."
- Who is the commander?
"The great Pit Fiend Habaal is the current commander of the Leviathan."
(He is the one the party saw at the very beginning)
- May we see this contract?
"I can retrieve it, if you so desire."
Later:
"If you have need of me, ask one of the lesser baatezu to send for
me. I am Grul."
The Leviathan is a huge mobile fortress, essentially a small castle on wheels, heading through the planes. The following are major areas of interest to the PCs.
1) Mess Hall
Where the fiends gather to eat and drink. In one corner is a magical everful barrel of Grog, where many of the baatezu get their drink from. At various times, the description changes:
Empty: "At this time the room that is apparently the mess hall is virtually empty. No one sits at the long tables, and the only nearby noises come from the kitchen, where it sounds like something is being chopped; or pounded."
Filling Up: "All of a sudden, all of the doors open and groups of baatezu stream in, in an orderly fashion. They pass by the opening to the kitchen, grab a plate, then head for the barrel propped up in a corner to fill their mugs. The fiends sit down and begin attacking their food, many of them talking between bites."
Full (most often): "Fiends of all types are engaged in a gluttonous feast on varying kinds of meat. In the corner of the room, propped up on a table is a barrel, where the baatezu seem to be getting their drink; it's quite a popular spot. There are few empty spots, but you might be able to squeeze in."
If the PCs investigate, they pass the empty brig, and enter the Torture chamber, where they see Belladonna. (insert a description here)
She is sweating, and looks
exhausted. A large needle is sticking out of her shoulder, held by
one of the beetle-like kocrachons.
"Once more, are there any other tanar'ri groups in the vicinity?"
the beetle asks.
"I... don't know."
"Why is your aura disguised? Were you about to embark on a spying
mission against the baatezu?"
"No..."
"Then why?"
(no answer. The beetle raises a scalpel to Belladonna's cheek.) "Why?"
"My mother..."
"Yes?"
(She hisses, and the beetle moves to the other end of the table)
"Your name, alu-fiend?"
"Belladonna."
"No. Your name is prisoner. Your name?"
"Belladona Digitalius, of the Tanar'ri ariel force."
(A cut, and another hiss)
"You are simply Prisoner. You will address everyone on this vessel
as 'my supreme baatezu overlord.' Is that understood?"
(no response)
"Prisoner, where in the Abyss do you come from?"
(no answer, and another cut)
"Prisoner, if I have to ask every question twice, this is going to
be both very time-consuming for me, and very painful for you."
"Tophetus."
"That is on the 76th layer, by the Guvner's counting, is it not?"
(a nod)
"What is the militia guarding Tophetus comprised of?"
(no answer, and the needle is driven in deeper and twisted)
After a while:
"A small spinagon crawls along the side wall. 'Dysfor, you're wanted
in the engine room."
"Well well, finally. Looks like you get a little break, prisoner."
The kokarachon turns to your group. "Help me get her back to the brig.
If she resists, kill her."
She is uncooperative, but does eventually go.
Grul, Cornugon Assistant: Standard Cornugon statistics. Arrogant but loyal, and will not hestitate to turn in anyone who threatens the commander (whoever that may be at the time). He doesn't mingle much with the PCs, preferring to stay by his master's side.
Kamsa, Gelugon Wizard: Hangs out mostly in the war room or the
control center.
Spells:
Level 1: Chill Touch, Magic Missle (x2), Enlarge, Wall of Fog
Level 2: Mirror Image, Melf's Acid Arrow (x3)
Level 3: Acidic Blast (x4), Chillball
Level 4: Ice Storm (x2), Fire shield(chill), Wall of Ice
Level 5: Wall of Iron, Hold Monster, Cone of Cold, Animate Dead
Ipok, Spinagon Messenger: Impatient, knows very little beyond what he is told to do, but likes to be the vessel that the leaders give orders. On some of the weaker-minded baatezu, he even makes his own orders, claiming they come from the high- ups.
Pannem and Edax, Spinagon and Barbazu cooks: Grim fellows who simply do their job, and don't speak unless spoken to. Edax thinks the duty is beneath him, while Pannem has been threatened that if he doesn't 'shut his yap', Edax will shut it for him.
Bakka, Rough Barbazu who gets into fights:
At some point in the adventure, when the PCs are eating, run this encounter:
"An ugly wiry-bearded barbazu catches your eye, as he strides in,
pushing a spinagon off to the side. He walks over to your table and gives
you a sneer, looking over your plates. Finally, he leans over, and sticks a
finger in (one of the PCs)'s food, pulls it out and licks it. 'Thank you
for saving me the trouble of waiting in line, chum. Why don't you go pick
up something for yourself,' he says, reaching for your plate."
Menides, Tiefling: Signed on the blood war allegedly to find his father, and
then kill him (for the death of his mother. Former Mercykiller). Claims the
father is a tanar'ri, but in reality he's a baatezu (Cornugon, Paxilus)
aboard the Leviathan. Does not know PCs were tricked, but does know this is
a suicide mission, and will freely reveal the information if asked.
Relatively friendly as long as he isn't crossed, keeps to himself though,
and very driven.
Calls himself The Sword Spider
Appearance: Has scales, clawlike hands, fangs, and a small tail
(hidden).
Equiptment: Has an electric-chain mail, and helm of the insect, and a
Cloak of the Arachnida
Minx, Erinyes:
Extremely pleasant and personable, seems even kind to the PCs,
in contrast to other people here. Don't believe it. She's cold and
manipulative, but a fine actress. Relatively new as Erinyes go.
Knows the PCs were tricked, but will not reveal this information.
Knows this is a suicide mission, and does not want to die, so plans
to desert. Also flavours her phrases with Sigil-slang, showing that
she's been there.
- Wants to know whatever the players know.
Possible First Meeting:
"Excuse me, cutters. Is this seat taken?"
"Good. It's so rare to find civilized people here, among the
barbazu and spinagons. They're such unrefined creatures. I'm used
to at least dining with the more intelligent baatezu, but that was
because my previous master... made an exception in my case. My name
is Minx, by the way. I've seen you around the last few days, but I
don't know your names...?"
"So, tell me, whatever possessed you to sign on to a baatezu war
engine? You must be either very brave, or very foolish. Want to make
a name for yourself in the history of the Blood War?"
Habaal (first commander), Pit Fiend: Very overconfident, makes overuse of the s sound in his speech. Knows casualties will be high, but firmly believes the Dark Brigade will succeed.
Caligula (second commander), Pit Fiend: Ambitious, next-in-line to be commander and will do anything for the spot. Cruel, enjoys torture as a hobby.
Belladona, Alu-Fiend Prisoner (only around after the attack): In the brig. Wears a mark of undetectable alignment. Begs PCs to help her escape. First question is, "Why are you working for them?"
Misc Encounters: Gambling with baatezu.
1) Entering the Gray Waste
(bells ring, people have to come out of private holes (no teleporting), etc)
"The ringing of bells resounds throughout the halls. The sound is deep like the bells of church, yet is somehow tainted, impure. They ring again, and a third time, then fall silent."
If the PCs are in a public place, a Cornugon appears near them, then gets ready to turn away. If anyone in the know is asked, they will reveal this information:
"The bells signal that the gate to the Grey Waste has been sighted. All baatezu must exit the unconnected portions of the Leviathan, or else they/we'll be trapped there while we cross the plane. Teleportation rarely works in the Grey Waste, and never in Oinos, the first layer. Pay it no heed."
A few minutes later:
"The Leviathan shakes violently, as though it's about to fly apart in
all directions. Suddenly, for an imperceptably brief moment, both it and
you cease to exist. When you return, you are only aware that something
has happened. Everything around you seems a little less there, as though
the colors, the textures, the sounds are muted just a little bit. The
Leviathan continues to roll along as though nothing has happened."
2) A tanar'ri patrol attacks
(vrocks, etc, have to defend from battlements)
This encounter should ideally take place while the PCs are eating in the
Mess.
"As you are eating, a small gargoyle-like baatezu, of the type you've come to know is called a Spinagon, flies in carrying a military fork. It puts two fingers of one hand into it's mouth and lets loose with a shriek of a whistle. 'Battle stations, everyone! Tanar'ri scum have been sighted approaching the Leviathan. Confirmed vrocks and succubi, with ground support likely.' Among the wiry-bearded barbazu, a deep cheer sounds, and they file out quickly."
If the PCs dawdle, Ipok comes over to them, taps one of them on the forehead, and says, "You berks are expected to fight, too, you know. You have to earn your keep like the rest of them." Minx rolls her eyes at the command, but heads off. Menides readies his blade and says, "It is a good day to die."
The combat: Players have their choice of many ways to fight. The towers offer a good vantage point for magic or missle attacks, but they are prime targets for retaliation. Fortunately, no more than one vrock or two succubi can assault a single tower.
Ground support includes many dretches and manes, with a few Marilith sorceress leading them. The group gives the impression of having been whittled down, and many more intelligent tanar'ri have been affected by the Waste, and are allowing themselves to be slaughtered. An alu-fiend is among the attackers- she attacks halfheartedly, and is captured alive (This is Belladonna, detailed more in the Torture Chamber).
Scenes to be seen during the battle:
After the battle, if they were of any help, Habaal asks them to share dinner in the private dining room, with Caligula, Grul, Kamsa, and other heroes of the day.
3) Encounter a lost baatezu squad.
The PCs might find the mess hall a little bit rowdier than usual, as a group of baatezu come aboard.
"The mess seems more occupied than usual, and the atmosphere even seems a little more festive, like a celebration."
- If the players ask, "We just took on a group of our comrades who were lost out here after slaughtering a tanar'ri squad. They're joining the mission!"
4) Yugoloth delegation
One Ultroloth, Two Nycaloths, and Four Mezzoloths. PCs are to escort the party to the command center, where negotiations are to begin. If the PCs are craving combat, the Yugoloths can have been hired to betray the baatezu, and attack when negotiations are complete. A small force is hidden outside.
5) Caligula's pitch
Must run this before the Leviathan leaves the Grey Waste, or else he'll be able to teleport away or gate in help.
At some time when the PCs are alone, they are contacted by Ipok. "Psst..." "Hey, you. You're wanted in the war room." If the PCs are amenable, Ipok shows himself and offers to lead the way. Once there, they meet Caligula, a large pit fiend a custom-designed greenish-metal helmet.
If pressed, Ipok will admit they are not required to attend, but they are highly encouraged, and they will be compensated for their time. Upon encountering Caligula:
The pit fiend turns from his maps and stares you down. "This is not for your ears," he says to the spinagon who brought you in. A towering insect-like fiend escorts the small creature out of the room, leaving you alone with the fearsome Pit Fiend. As he speaks, he occasionally will dip his hand into a bowl, which appears to be filled with small mealworms, spear one with a claw, and pop it into his mouth, still wriggling.
"It has been several weeks since I last snacked on a pitiful mortal," he says, watching your faces. "Oh, don't be alarmed, as long as you work with us, I don't seek to harm you. It is merely an observation. You are of use to me, and I'm sure I could see to it that I am of use to you."
"The current commander of the Leviathan is Habaal. I believe you've
met him already. The simpering old fool never had much battle experience,
so I don't know how he got this assignment. He doesn't have the type of
leadership required for a mission of this magnitude."
- You do?
"Of course I do. And were I only to gain the chance, I could prove
it... I am second in command, however. The commander would have to fall
victim to some sort of... accident, for me to take charge."
(He wants to PCs to suggest removing him by force If they need
more encouragement, or details, he mentions the following.)
"You know, Habaal has a bath every evening, like clockwork. He's all alone in there. Why, if someone was to sneak in with the intent to kill him, there would be no one else to stop him. It's a shame the Commander is so... lax. I've tried to warn him of the dangers, but he doesn't listen. Tsk tsk tsk..."
Once the PCs make an offer of some sort:
"Well, I can't condone such an action, but as it would be better for
the mission, if you were to go ahead with it, I would not turn you in,
either. And were you caught.. well, I've always wondered what I would do
if I were placed in the uncomfortable position of passing judgement on the
assassins responsible for the death of my predecessor. I suppose in a
case like this, I might take the overall benefits into account, and
let you off with a relatively minor punishment... say, exile from the
Leviathan. Hypothetically, of course."
"And continuing this hypothetical train of thought, if you were to attack him as you are, you might surely die, and you are vital to the completion of the mission. Therefore, one could make the arguement that, if you insist on this endeavor, I would be best serving my people by providing you the means to succeed. Do you find my logic sound?"
- What help can you offer?
"I could provide you with silver weapons; Iron is no good against our
kind, but silver bites almost as much as steel bites you frail mortals.
In addition, I would be inclined to donate one amulet which allows ANY
weapon, no matter what the make, held by the wearer to draw Habaal's
blood."
- What about the contracts?
"Well, I believe the contracts say something about serving in a
baatezu way... among our people, killing a rival is not breaking the rules,
as long as one isn't sloppy about it. If he hasn't specifically ordered
you not to attack him, no one can really say you were disobeying orders,
am I right?"
- How can we do this?
"Habaal takes a bath every night. Someone with authority, if they
were inclined, could arrange for his few guards to be 'preoccupied' at a
certain time. If someone managed to exploit this time, they would find
him completely alone. If something like this were to happen before we
leave the Grey Waste, he could not teleport away, nor could he summon
aid from Baator."
- What's in it for us?
"Are you asking me to hire you for such a dastardly act?"
If the PCs seem extremely reluctant, he also makes the following comment:
"It might interest you to know that the projected number of survivors
from this mission is zero. There is a slim chance of success, and we are
taking the risk... but our chances would be infinitely greater if someone
competant was in charge. All in all, though, the greatest chance for
survival lies in being discharged from the Dark Brigade."
6) The Leviathan stops
(allowing PCs to investigate the engine room, and/or kill Habaal, meet the
alu-fiend (mother named Jeh) (who seeks escape and isn't really evil))
"There is a great, unnatural squeal coming from outside, and you are suddenly thrown toward one wall. It takes a moment before you realize what has happened. For the first time you can remember, the Leviathan is not moving forward."
If PCs have accepted the mission to kill Habaal:
"Amidst the confusion, the small red spinagon flies out from a hole
above your heads. 'Oh, good.' it says, as it hands you a piece of
parchment, folded in two. 'I was told to deliver this to you, and uhm...
what was it... oh, yes, you have to open it in your room.'"
If the PCs open it anywhere outside their room, it is a blank piece of parchment. If they go into their room and open it (Menides is there, unless asked to leave), a fanged mouth appears on the paper and speaks...
"Now is the time to strike against Habaal..." And a small map shows what route to follow to find the bathing chamber.
If asked, Caligula claims he knows nothing about stopping the ship, and is indeed telling the truth.
If the PCs have not accepted the offer, or if they have succeeded:
In the hallway, the PCs are stopped by a Cornugon, who grabs one of
them by the clothing, and barks, "You! Mortals! Go down to the engine
room and see what's causing the delay! The Master wishes to be on our
way."
In the Engine Room (pass by the brig):
"This room is filled with what looks like humans and elves, in varying
amounts of pain and suffering. At one end of the wall there is another
figure, who appears to be locked to the wall somehow. There is something
about this figure you can't quite place.
(If the PCs get closer to the figure):
"As you get closer, you realize what it is. You can almost feel a
physical sensation of goodness and light as you get closer to the figure.
It is manlike, but with angelic wings pinned against the wall by it's
back. Nails hold the being, at once noble and pitiful, to the wall.
The face looks worn and old, the body is tired, and the wings are
beginning to lose their feathers. Nevertheless, it is a creature of
supreme beauty, especially in a place such as this."
A beetle-like fiend with a long proboscis and wearing a spattered apron, waddles over to the angelic being, who appears to be unconscious and breathing only very shallowly. The fiend dabs a wet cloth over the being's head, and on the wounds on the arms and legs, then waddles back to a metallic tray.
If PCs asked why the Leviathan has stopped moving:
"The beetle-creature gestures to the angel being. 'I know my patients.
If we give him any more now, he'll die. No more breath to scream as is.
Need rest, maybe healing. Any of you able to heal a celestial?'"
Another, identical looking creature walks up to the first. You hear the
echo of its thoughts in your mind, clearly directed it's colleague. 'What
about the new prisoner?'
'The tanar'ri half-breed? Never feel pain, never make good symphony
to move. We'd move faster if we all got out and pushed.'
'This one's different. Real screamer. Maybe little too much human
in her.'
'No. We wait, let our prime patient rest. Few hours delay, then
we will be on the move again.' The kocrachon takes off the apron and
throws it on the tray. 'Meal time, anyway.' He walks out, leaving his
apparent assistant to merely putter around.
If the PCs approach the celestial:
He is at the present unconscious, but if the PCs make any effort to wake
him or even get his attention, his eyes open slightly, barely even
looking. He is responsive to questioning.
Questions:
"Who are you?" 'Jibril.'
"What are you?" 'I am a deva from Elysium.'
"How did you get here?" 'Was on assignment in Baator... Ambushed.'
(At some point, if the Pcs ask a question you don't feel like answering:) 'Please... if you have any goodness, release me from their service. Even in death I would be happier than now, for at least I would not be in the service of evil."
If the PCs explain about the contracts: 'I understand. I cannot reasonably ask you to place my soul ahead of your own lives. At the very least, if you get off this vessel, I implore you; tell others of my kind what you know. They should have dispatched a rescue... For a moment, I thought maybe you were that rescue... but it seems not. Perhaps they do not know where I am being held.'
"What are they using you for?" 'They use me to make their infernal machine roll. They torture my body until I cannot help but scream.. no small feat against a celestial. I'm a little ashamed... I always thought I could hold out longer against torture. (coughs) I guess not.'
"What does that have to do with the Leviathan." 'My screams drive this abomination forward.'
If the PCs explain about their memory loss: "The waters of the Styx? If one of you will touch me, I can attempt banish their influence."
If any of the PCs touch him after mentioning the Styx, they get the
following vision (adapt for whichever PC does it):
"A sudden wave of dizziness engulfs you, and you feel as though
you are going to fall. Suddenly, you find yourself back in Sigil,
being led into a stately manor. Once you get to the sitting room,
three men, all balding and wearing white robes with gold trim,
are already waiting for you.
'We have asked you here to ask if you'll undertake a mission. One
of our agents has fallen into Baatezu hands. You have dealt with the
baatezu before, have you not?'
'Yes,' you hear yourself answering.
'Then you know of their dangers. They are very cunning and
manipula...'
The dizziness overwhelms you once more, and you stumble a step
back from the deva. His eyes are now closed, but he still breaths.
What little he's done has exhausted him.
7) Passage to Carceri
"Another shift takes place. This time your stomachs feel like they're squeezing in, but colors seem to drain back into everything. When it is over, for a moment, you're overcome with a feeling of claustrophobia, and the thought that you'll never ever escape; though, the thought fades quickly, and you're not even sure what you feel you'll never escape FROM. The Leviathan keeps moving."
8) Minx's desertion
Sometime while on Carceri: PCs might hear Minx outside their room. She casts a sleep spell, with the hopes that everyone will be affected, and then plans to steal anything interesting (and any money) and leave. If discovered, she claims she was trying to enlist the PCs help. Or, she volunteers to provide backup to the PCs when they open the gate to the Abyss.
9) Into the Abyss
Must get out each time to activate the gate.
a) - Demogorgon's Layer
Watery. A section the PCs are in may get flooded and swarmed with baddies. There were a bunch of cool giant fishies in an issue of Dragon magazine, that's where I used the stats, but I'm sure other people can find suitable opponents.
Sea-dwelling baddies (Saughin(?)) attack the ship, and manage to break open one of the seals on the tower.
A kraken latches onto the Leviathan and keeps it from moving at any high speed.
Flavour text: When PCs are in a hall, "You hear a slight rumbling in the distance, gradually increasing."
If the PCs do nothing: "Suddenly, a door bursts open, and a wave of water floods out, covering the immediate floor. The water doesn't stop there, however. It keeps flowing. It's ankle-deep, and rising fast." (If it gets to be any significant depth, the PCs may be afflicted with Lampreys, or attacked by fishmen)
Leaving The Layer:
The exit to this layer is a huge expanse of coral, which looks to be naturally formed. The PCs are asked to swim out ahead of the Leviathan and activate the gate (by spilled human blood). Unfortunately, the area is a magnet for large fish, some of whom are likely to attack the PCs if they try. (Fish are from Dragon Magazine, #235)
b) - Layer of insects
Layer is completely composed of insect life of various forms crawling all over each other. (Insect armor from Dragon Magazine Annual 1 as a possible prize) -Teleporting tanar'ri, but not very many... some may attack the engine room here or in next scene.
c) - Relatively normal layer, populated. Short duration.
d) - Target Layer
- more attacks (guards)
- Tiefling tries to kill his father while the PCs are in sight. They can help him, help his father, or neither. So long as they don't fight against him, Menides dies dramatically as he kills his father... asks that one of the PCs promise to try to find Paxilus on Baator and kill him once and for all (Baatezu killed off their home plane are merely banished to Baator for a period of time). Something in Menides' tiefling nature prevents healing spells from working on him.
10) Assault on a Tanar'ri city
The PCs are told to go into the city up ahead, scout, and sabotage their defenses. If they succeed, they may leave, but they won't be paid.
I'm not the greatest DM in the world, but I enjoyed running this, and I think the players had fun. In this adventure, I included two possible hooks for other adventures: 1) Menides' dying request, to finally kill Paxilus, on Baator, so it's final. If they players are the kind to honor a dying man's last request, they'll do it. 2) Not listed above, the moment the PCs got back to their rooms after they 'woke up' at the start, they checked their belongings. Being a benevolent DM, I didn't have them missing anything (except for a few spell components in the case of the wizard.. nothing serious though, as we don't enforce those rigorously), and even gave them a bit of extra gold for their troubles... then, inspiration struck, and I told them they found a small black box that was warm to the touch. They could do nothing to open it, and though detect magic would indeed reveal that it was magical (very powerfully so, in fact), nothing would tell them what it did or how to use it. Even Identify failed to provide information. They assumed they got it during one of the missing 3 days. I never really got to develop it, and to this day, I'm not sure whether I'd have preferred to have it be some mysterious artifact that was the key to another adventure, or some baatezu trap/homing beacon or something. Anyway, if you run it and want to use the same trick, tell me what you come up with. :) They did spend a lot of energy trying to figure out what it was.
Another thing I made up on the fly was the game the barbazu gambled... one of my players wanted to join in. I improvised a game based on rolling 3 (or 4? It was over a two years ago, I can't remember it exactly) d4s, and betting on the results (ie, 3 of a kind, etc), with different 'odds' for more unlikely rolls. As it was all improvised, I couldn't actually do any detailed odds analysis, but neither could the player so it worked out well. Later, I did some and realized that some bets were far more likely than others. Still, it was an interesting game. Also, the barbazu who didn't have gold bet things like parts of their beards, or their own fingers (or those of others, won in other bets... one of them had a necklace of fingers from other barbazu, ripping them off whenever one was required. I can't remember the exact values. I think fingers were worth 50gp.
I made up written contracts to show them when requested, and considered filling a small tray with gummi worms for when they were talking with the Pit Fiend. In the adventure, I made the assumption that the contracts were fake, though I didn't write it into the text in case they wanted to leave the Leviathan right away and risk the curse. So, though they were never actually bound, they thought they were, and that was all that mattered at the time. However, as an interesting twist of fate, near the end of the adventure, our resident wild mage had a surge that seemed to have no effect. What actually happened was that he was given an 'illusionary disease'... that started slowly and progressed, giving illusionary boils and such as a real disease would, and, since they were in the Abyss, I gave it the added taint that the illusion was contagious by touch. They noticed the first visible signs after they finally left the Leviathan... thus, they thought the contracts were real, and this was a result of that. I was quite amused.
Also, as it turned out, they left the Leviathan on the insect layer (I moved up the fight between Menides and his father to just as they were leaving), so I never got to the last two layers, which worked just as well. They freed Belladona and Jibril, who accompanied them across that layer to find a portal to another part of the Abyss. All of them, save the Deva and Alu Fiend (whose magic resistance rendered them immune) had been infected by the illusionary disease, and the adventure ended as they entered that other portal, hoping to find a cure. We never had a chance to play again (at least, continuing the same campaign), so that image of them stuck in the Abyss, with a celestial and a fiend, knowing they're going to die soon, but at the very least glad they were getting off the layer of teeming insects, is the last I have of that group.
The water layer was fun, most of the group got swallowed whole by the giant fish... one escaped by casting a fireball from within the creature's stomach.
Anyway, that's all I can think of right now about the adventure.. it was a while ago, as I said. However, feel free to give me your thoughts, especially if you take the adventure and run it, however altered you might make it. (Yes, you're free to alter it for your own needs. Just don't distribute it altered and claim I did it. :))