"I think Darvin should drive, he must have worked out the controls the best to catch the most tortured souls." Offers Drabash, showing no real interest in the driving.

A driver proficient with land vehicles can add its proficiency bonus to ability checks and saving throws made using the infernal war machine’s ability scores.

Only Tibi and Drabash have this proficiency.  The Tormentor only holds 4 people inside it so Tibi will need to fly to cross the river if you are taking Krikendolt along as a guide. 

As you examine the machine Krikendolt explains the operation of the machine.

Tormentor

A creature can use an action of the station it’s occupying. Once a creature uses a station’s action, that action can’t be used again until the start of that creature’s next turn. Only one creature can occupy each station.

A creature not occupying an action station is either in a passenger seat or clinging to the outside of the vehicle. It can take actions as normal.

Creature capacity describes how many creatures can ride the infernal war machine comfortably. More creatures can fit by squeezing or by clinging to the outside of the vehicle.

Cargo capacity specifies how much cargo the infernal war machine can carry.

Helm

The helm of an infernal war machine is a chair with a wheel, levers, pedals, and other controls. The helm requires a driver to operate. An infernal war machine with no driver automatically fails Dexterity saving throws.

A driver proficient with land vehicles can add its proficiency bonus to ability checks and saving throws made using the infernal war machine’s ability scores.

Drive. While the infernal war machine’s engine is on, the driver can use an action to propel the vehicle up to its speed or bring the vehicle to a dead stop. While the vehicle is moving, the driver can steer it along any course.

If the driver is incapacitated, leaves the helm, or does nothing to alter the infernal war machine’s course and speed, the vehicle moves in the same direction and at the same speed as it did during the driver’s last turn until it hits an obstacle big enough to stop it.

Bonus Actions. As a bonus action, the driver can do one of the following:

• Start the infernal war machine’s engine or shut it off.
• Cause the infernal war machine to take the Dash or Disengage action while the vehicle’s engine is running.
• Insert a soul coin or pour a flask of demon ichor into the engine’s furnace (see “Soul Fuel” and “Demon Ichor Boost” below).

Weapon Stations

Each of an infernal war machine’s weapons takes up a station on the vehicle.

Tibi looks at Drabash with a grin and says “looks like you’re driving cos I ain’t getting in that thing!”

Drabash says "Well if it's me or Tibi, and Tibi's gotta fly, then I guess its me to drive. So," he says to Bazelsteen, "Is this thing is waterproof? Has it been tested on the bottom of the river so it won't get bogged? And is it loaded, in case we need to fight?" Assuming he gets affirmative answers to all of these questions, he tells the others to get in and takes up the helm. "Who's on the Harpoon launcher?"

"I can do that," Darvin says. "Where are we going again? I know it's only been a few hours, but it feels like weeks somehow. Must be an effect of being in that damned contraption under the river for so long."

"Its loaded, waterproof, it won't get bogged, it runs great.  Just drop a soul coin in and you are fueled up and ready to go."

Drabash settles in behind the controls at the helm and Darvin sits at the controls to the harpoon launcher.   Kaelani and Krikendolt strap into seats and Tibi sets off to cross the river.

Driving down the bank you splash into the water and churn across the bottom.  Its hard to see but you keep your bearings well enough that after several minutes you come out the other side at about the same time as Tibi reaches the other side while flying.

Drabash hits the gas as you reach dry ground and quickly start to outpace Tibi, who even when dashing as fast as he can, has a hard time keeping up.  Fortunately Darvin is paying attention and calls to Drabash to slow down and Tibi is able to catch up.  He then clings to the outside as you speed across the landscape.  

A couple of hours later and you reach an iron tower that rises atop an island on a lake of boiling blood. No windows penetrate the tower’s walls, and its only visible door opens onto a high balcony. Red lightning crackles constantly between two horns of metal on the tower’s roof.  You see a number of creatures milling around at the edge of the lake and count out nine mezzoloths and three nycaloths present.

"I told ya I would get you here." Krikendolt says.   "Mordenkainen pays yugoloths to carry out his bidding in Avernus. His wages are so attractive that these fiends have taken to gathering outside his tower when he appears in Avernus.  The fiends aren’t looking for trouble.  They’re more interested in landing a lucrative contract with the mage.  I'm hoping I can find better work myself.  That last job sucked."

 Tibi walks up to one of the nycaloths and says "Captain Cracticus Tibicen of the Flying Fists mercenary company at your service. So what sort of work exactly is it that this Mordenkainen fellow hires you for?"

One of the fiends looks back at you.  "Finding things, sending messages, whatever it is he wants done.  And he pays well." it responds.

At that moment a stern, bald man with a neatly trimmed black goatee beard and a penetrating stare appears at the balcony. He looks down towards you.

"Hmm, interesting.  An Aarakocra, a Half-orc, an Aasimar, and a Changling stand before my tower."  As he says this all of the fiends assembled turn their attention to you.  "An eclectic collection of beings the likes of which I have not seen in quite some time.  Tell me, why are you here?  You cannot be here simply to run my errands for me.  Speak up!"

At that moment a stern, bald man with a neatly trimmed black goatee beard and a penetrating stare appears at the balcony. He looks down towards you.

 "Hmm, interesting.  An Aarakocra, a Half-orc, an Aasimar, and a Changling stand before my tower."  As he says this all of the fiends assembled turn their attention to you.  "An eclectic collection of beings the likes of which I have not seen in quite some time.  Tell me, why are you here?  You cannot be here simply to run my errands for me.  Speak up!"

 Tibi bows to the man “Cracticus Tibicen – Decionist of the Baldur’s Gate chapter of Acquisitions Incorporated at your service. As to why we are here, we seek a sword plunged into a rock at the climax of a great battle between fiends and angels, which it looks like the angels lost!”

The man ponders for a moment. "So you seek Excalibur, the sword in the stone that made Arthur king?"  He mutters for a moment and furrows his brows.  "No wait, that is not it.  Another plane of existence that had nothing to do with angels and fiends."  He looks back at you.  "I know of no stone that holds a sword.  At least not one here in Avernus if that is what you mean."

Lulu flutters up next to Tibi and the man laughs, "And a Hollyphant!  Amazing!"

Lulu, undaunted calls up to the man, "We seek the Bleeding Citadel and we were told you know where it can be found."  

"Eh?  The Bleeding Citadel?  I do not know the location of the Bleeding Citadel, nor do I care to find it.  But the balance will be maintained in the universe.  There is a..." and he pauses a moment, "a lesser mage who also studies the workings of magic in Avernus.  He is a mage of no renown who haunts the site of an obelisk.  Seek him, he may know of that which you seek."

"This obelisk, where might we find it" Tibi asks. He thinks for a minute "oh and by the way if I come across a rock with a stone poking out of it I'll be sure to let you know!" Tibi turns away from the man and then turns back as if he had just remembered something "you're obviously a well traveled man, have you ever heard of a country where I remember reading they select the king by some watery tart throwing a sword at him!"

The man laughs, "Listen. Strange women lying in ponds distributing swords is no basis for a system of government."  He then points northwest "That way.  Cross the Pit of Shummrath and you will find it. Its a lake of green slime. You can't miss it."

Tibi grins at the man and then turns to the parry "right gentlemen looks like we need to head northwest towards the put of shummrath - so let's get cracking!" as he heads off in said direction.

Drabash says, "OK lets get going." and climbs back into the Tormentor. He checks to make sure that everyone but Tibi is inside and has done their seatbelts up. He then speeds up in the direction Tibi was heading, slowing down marginally to let Tibi catch hold and then continue towards the lake of green slime.

Krikendolt says his goodbyes as you ready to leave.  "I've guided you here as promised.  I'm going to stay and see if I can get work from the mage.  Good luck!"

You head back out across the landscape and it isn't long before you see that a deep rift slashes across the surface of Avernus for as far as the eye can see. As you get closer you see that the canyon is over a mile deep and filled with a lake of green slime that undulates as though breathing. From a nearby cliff, a tributary of the River Styx cascades down into the slime.

You see a natural rock formation creates a bridge across the chasm near the western end.  Across the bridge an obelisk ringed by smaller standing stones rises from the crest of a hill. 

Dangling from a bent iron crane that leans out over the chasm is an iron cage containing a hairless, green-skinned humanoid wearing shackles on its ankles. The crane lowers the cage by a chain into the slime, immersing the creature in the goo for a minute before hoisting it back out. This dunking continues again and again, and the trapped creature seems helpless to stop it.

When they get closer Tibi flies over and starts circling the cage and the creature. As it starts to come back up he yells out "well you obviously pissed somebody off - what exactly did you do?"

As Tibi flies up the fiend starts communicating with everyone as they hear its voice telepathically in their heads. "Help me!  I was imprisoned by a pit fiend for stealing soul coins. My name is Baazit.  If you free me I promise to show you how to form magical servants from the goo."

"If we free it, we may incur the wrath of the pit fiends that imprisoned it in the first place. If this is punishment for a wrong-doing he admits to doing, perhaps justice should be allowed to continue..." Kaelani says as he looks with disdain upon the creature.

Tibi shrugs his shoulders "they say gentlemen that one should leave sleeping dogs lie and while he's obviously not asleep its not our fight and I agree with Kaelani here so onwards and backwards - hmm?"

Drabash responds, "Magical servants, what can these magical servants do that we couldn't do ourselves?" he says while flexing his muscles, though feeling a little discomforted by the method of communication.