This mod adds a few new creatures, a bunch of interactions, and a whole lot of potential fun. Dwarf Fortress meets Lovecraft. Encountering an elder god in the lower caverns may cause a hidden cultist to appear among your population, who will cause strange things to happen in your fortress - pools of slime and piles of tiny fish skeletons will show up in the halls, corpse pieces will sprout legs and tentacles and begin to scuttle around, fish will grow aggressive and start to walk about on land, and one by one, your citizens will start to turn into the Deep Ones, monstrous fish-frog people. The effects will grow more frequent every year. You have three years to find the cult leader and kill them before all hell breaks loose...

Based on Meph's Cult of the Carp God for Masterwork.