Bone Welder

It sits in Dungeon chests, and unlike almost every other special item down there it can appear in any chest type rather than only the locked gold ones. When a chest has it, it is always the last thing in the list, so it is easy to miss if you are grabbing the top rows and moving on.

Fishing will not produce it. Nearly every other notable Dungeon item eventually comes out of crates, but this one never does, so a world without one leaves you two options: buy it from the Steampunker while she is living in a Graveyard, or go raid another world's Dungeon and carry it home.

It gates the entire bone furniture line and the Gothic set, which is a lot of building material to hang on a single item with no backup source. If you also want the Dungeon shelves, stand it inside Ecto Mist, since that recipe wants both at once.