NSSB by NPX Team is a mapgen mod for Not So Simple Mobs (NSSM mod) that adds a new underground biome called Morlendor, and also spawns 20 new structures throughout the world for multiple mobs.
Forum page: https://forum.minetest.net/viewtopic.php?f=11&t=14135
Yeaaaaah, I've been waiting for this
finally a mod that adds new structures to the Minetest Game, thanks. Now what's left is making a villages mod that works correctly