The Faerie Coffins works perfectly as both a self contained adventure or as the begining of a larger plot.
The horror elements of this adventure are handled really well, as it's not a simple gore blood fest, but rather a well developed sense of suspense and mystery. The new stat blocks really help as the players won't know what they are fightning with. The whole adventure takes place inside an abandoned Inn with many interesting rooms, the characters can interact with it in many fun ways while they are followed by creepy dolls.
The adventure also contains new magic items that are thematic and interesting, my favorite is the Sword of Blood Horror which is totally not what it sounds like.
The story is driven with the characters following and collecting creepy dolls all over the inn, with their tiny steps and creepy sounds guiding them from place to place. This is great to move the story forward and to give a clear objective.
Minor nit picks that can be easily edited:
- Area A describes six doors leading away from the room. The map shows only 5 doors.
- The characters can learn about the Nulfidar's past connections to the Feywild, but how they learn it is handwaved rather quickly. I would love to see some more descriptions.
- One portrait says "Elustrial Silverhand". Pretty sure it is supossed to be "Alustriel". Loved the cameos tho.
- Alongside the first mention of Garl Glittergold, there should be a brief description of who he is. I know he is the god of gnomes, but a (god of gnomes) would be cool to see.
- This adventure contains a lot of magic items from Xanathar's Guide to Everything. While I have the book, some others DM may need to replace them with trinkets.
- Finally, I think this adventure contains maybe too much treasure for a Tier 1 adventure, though not everyone will be running it as part of a larger campaign.
- The adventure could technically end really quickly if the characters find the trapdoor leading to the "final boss"