The cooperative overland crawler Dungeon Degenerates: Hand of Doom just received a new supplement that allows players to travel underground beneath the Ghostgates in search of treasure. The tunnels are part of a dead fish-shaped structure, and the enemies lurking there are of the watery, slimy kind. This scenario was written by Eric Bouchard and illustrated by Sean Aaberg, and is available to purchase from Goblinko.
Unfortunately, Gold and Grime at the Ghostgates has some printing errata (missing rules), so if you order it, make sure to check this thread for the omitted text. The module works somewhat like a choose-your-own-adventure booklet, with various paths and encounters you may have depending on your decisions. A scroglin guard enemy card is also included in the package.
You can see it in detail in this video by the Dungeon Dive: