Deep dark dimension mods featuring the link below

A Minecraft mod which features more blocks, items, armors, and hidden mysteries to complement the Deep Dark biome.

adds a new dimension accessed via the ancient cities in the deep dark biome

Arda's Sculks mod is a mod that improves the ancient city in the game and offers the ability to open the ancient portal in the ancient city. This mod adds many deep dark biomes to the game and many boss creatures found in these biomes.