I was going to skip this one due to the amount of work needed to convert this for use in Ptolus, but decided to give it at least a cursory try. This adventure is the 5th and final episode in the Mere of Dead Men series that were published in Dungeon Magazine during the 2nd edition period, and it is an adventure that I particularly enjoy reading. The module is extremely wordy, filled with a ton of backstory and history before you even get to the adventure itself, fortunately this information is not needed to convert the scenario.
There are twin brother adult black dragons that make a well coordinated effort to leave the impression that there is only a single dragon involved. They are after the bones of a long dead ancient black dragon who had become a dracolich.
The brothers have located the tomb complex and now need to manipulate someone into going in and bringing the bones and remaining ghost, out to them.
Worshippers of Father Claw are also after the bones of the Ebondeath, and powerful magic items within the mausoleum, and while the brothers have been manipulating the worshippers, they would prefer their own team of delvers get there first.
In the module as written the adventure takes place in a vast swamp with all sorts of obstacles and nasty encounters before reaching the tower and mausoleum site. Placing the adventure in the dungeon and caverns below Ptolus is the obvious thing to do, and requires quite a bit of effort.
Starting at the beginning . . . A group of religious soldiers have been below the city trying to make an area safe for travel. Maybe we should change their objective so that their expedition was to prevent anyone from getting to the tomb. I'm tempted here to make these a group of mercenary delvers led by Ralelle Noramar, a knight of the Golden Cross. The knights of the Golden Cross were once dragon slayers. One of the dragon brothers attacked this group and has taken the survivors hostage.
Getting the player characters involved may be as easy as the Knights hiring the party to take supplies down in to the dungeon for the other delvers and to re-enforce them. They would arrive only to encounter the dragon and learn of the hostages. That's when the dragon offers them a "deal". Get what I want and you get your people back as well as most of the hoard of Ebondeath.
There happens to be a celestial event tied to the timing of getting into the mausoleum in the adventure as written. Perhaps this could be altered to be a double lunar eclipse of Lunas and Rogue, I don't know if the event should have any actual effect since the happenings are all under the city, but you could still keep it as relevant. Maybe the Knights of the Golden Cross are aware of the significance of the event to worshippers of Father Claw and are playing it safe by sending an expedition below. The idea for the celestial event itself is interesting and plays well with the setting.
It should be possible to keep some of the feel of the difficult trip through the swamp by having many of the cavernous areas partially flooded.
Keep the undead encounters, but change them to be more appropriate for the caverns, instead of having undead horses involved maybe skeletal lizards ridden by skeletal Drow.
Replace the shipwreck with something else of interest. Consider making the encounter take place in a former Kuo Toa outpost with zombie Kuo Toa.
There is a major encounter with a Dark Tentacles and some of its monster servants right by the tomb's location. This is going to be a tough battle on the shore or in a small underground lake. Depending on what system you are playing you made need to create the Dark Tentacles and its monster pals from scratch.
Finding their way to the tomb of Ebondeath will have been made possible by the party being given a few rings by the dragon. These rings in the adventure are needed to call the tower and mausoleum up from below the swamp. In this case they should cause the water flooding the cavern to recede, revealing these structures for a good number of hours after the celestial event. Another advantage of the rings is that the wearer is Invisible to Undead (minor ones at least). The rings also give the wearer some nasty powers, but making use of them can bolster the power of the temple, and potentially harm the user by reducing their maximum hit points by an amount permanently.
Keep the mudmen encounter (they can be called muckmen if that suits).
Father Claw's followers are also on the way to the location. The dragon brothers are trying to ensure they get what they want so there are rival delving teams. One of the brothers is sneaking along, hidden from both groups. It doesn't matter to the dragons which team gets what they are after as long as the bones of Ebondeath and a special crown become dragon property. Player characters have a two hour lead on the worshippers, so it is important to keep track of time spent exploring in case of a possible encounter of the teams.
The Uthtower should be converted to a large column that has been hollowed out to make rooms.
In the event the cultists get the bones and crown, one dragon will side with the PCs since the hostages are a hold on them that guarantees the dragons get their desired items.
All undead in the structures are either resistant or immune to turn undead do to the unholy nature of the place. Undead and worshippers of Father Claw also gain Protection From Good.
There are markings relating to Father Claw through the place. If PCs decide to deface these markings it will have an effect including shaking similar to a minor quake. It is possible to cause the structures to collapse if enough destruction is wrought against these markings and other items holy to Father Claw.
The rooms within the tower/column have standing water in them that rushes out when doors are opened, and this can be used for a moment of entertainment if someone gets swept off their feet and down a flight of stairs, but shouldn't be overplayed.
In the library the only undamaged tome remaining is a Book of Vile Darkness.
In the catacombs below the tower, the water level in the rooms drops by 2 feet per hour meaning the party has that obstacle to deal with if they try to explore downward before exploring the tower portion.
Originally these structures were used by royalty of some type and there are remains in the crypts for various noble houses. Maybe these were the crypts for an ancient settlement of Drow. Alternately it might once have housed dwarves.
There are undead down here to deal with.
Among the treasures discovered in the Ebondeath's remaining hoard is a means to destroy the dragon's bones, a Wand of Obliteration, but the PCs would need to figure out the command word which was lost ages ago.
Getting the bones out of the mausoleum and to the surface is a challenge. The bones are big and heavy, weighing a total of 3,000 pounds. There's a listing of the number of man hours it will take to remove them. Fortunately one of the worshippers of Father Claw has a Bag of Holding that will make it easier.
If the PCs uphold their end of the "bargain", the hostages are released.
There are plenty of plot ideas that can spin off from this adventure. The bones of Ebondeath may be able to take over control of one or both dragons and down the line that could mean more trouble. Giving the bones and crown to the dragons will free the hostages, but might in the long term make the Knights of the Golden Cross unhappy.
