My players characters are currently exploring some truly ancient underground ruins of a sunken city (the setting is Ptolus, if it matters), and the PCs are trying to find the sites of some temples of various gods to explore.

Next up on the list are temples of ancient gods of knowledge and magic, and when I searched for thematically appropriate monsters to populate them, I came across Nothics. They have a pretty good base concept, but I need some more ideas to make exploring a ruin filled with them interesting. Things I am looking for in particular include:

• D&D lore about the Nothics (this doesn't have to be from 5E)
• Ways of personalizing them and their environment, emphasizing how weird and creepy they are
• Variant stat blocks that might make encounters with them more interesting
• Creatures that might co-exist with them

But feel free to throw any ideas you have out here - I am still in an early brainstorming phase!