Little context before I tell this tale. I am the DM of a Homebrew Campaign based off Castlevania: CoD with Curse of Strad elements implemented due to similar themes. The party, only three members at the time, consisted of a Human Artificer (Corvus), a Naga Rogue (Kuhri), and a Varient Tiefling Warlock (Reverence). Corvus is a Criminal Mastermind. I allow Criminal Backgrounds to know Theives Cant since it makes sense.
Now to our tale. Trapped in Dracula's domain, no way back, the party presses onward through an abandoned castle. Well abandoned by the uncursed living as they encounter skeletons and undead. Entering inside a room, they find a single chest. The players, even with a newbie, find it suspicious. However, Corvus had a flaw I could play with. Greed. I have his player roll a Will Sav and fails.
Blinded by the thought of treasure, the Human ran to the chest and went to open it. Trapping the party inside as Skeletons come out of black portals from the ground. Combat ensues. Kuhri goes down. Then both sides started to roll horribly. It became a stalemate.
Reverence, seeing this was getting no where and low on spell slots, decided to try diplomacy. Seathed weapons and suggested that Corvus did the same. Begrudingly, he did. The Skeletons followed suit since they were not actually undead but cursed individuals. Something I came up with on the fly since I had not expected the party to be overwhelmed.
The Skeletons turned to Corvus, recognizing a fellow criminal, and began to use an ancient form of Theives Cant. They wanted to help Kuhri. This was relayed to the Tiefling before they moved to give the Naga a hunk of healing mutton. She instinctively swallowed as they stepped back since they didn't want to be crushed in her coils.
Luckily, Kuhri understood that no combat sounds meant these Skeletons were friendly. Corvus did, however, obtain boots that were enchanted. So it wasn't a total loss to open the chest. The doors are no longer blocked and they head on. Meeting more of these Cursed Folks and fighting off Fenrirs (Hellish Wolves) with the aid of their new buddies.
In time they come to another treasure room, this one not booby trapped with anything. Just had two things pivital to taking down the Dark Lord. Reverence gained a Fairy Familiar, Memphisyle or Memphy, that could unlock Cursed Chests. Kuhri gained an item that increased her maximum health. Corvus, however, recieved a rather cyrptic message upon exiting the room. Dracula offering him a bargin. He'd give him power and lift the curse on his relative if he crushed the growing rebellion in his domain. The Skeleton they had been more or less seen as the leader, sensing something wrong with the Human, shook him. Calling him by his real name, Crowley, in Theieves Cant with one hand. This snapped Corvus out of it. How did this Cursed Skeleton know that?
He didn't get what it all meant at first but would after Memphy opened a chest. The party found an item that would serve them later and give magical powers to a non-magic user. The Skeletons, however, found items belonging to them. One item was armor, armor baring the family crest of Corvus' family. Armor belonging to his great-grandfather.
It made sense to him now, how this Skeleton had known his real name. And now he was conflicted. Did he listen to the Count or beat the decay out of the Vampire Lord and force him to lift the curse? So far, he's chosen the later. Will it stick? Who knows. We have many more sessions ahead.