A Dungeon Core is, quite literally the core of a dungeon. Like the brain and soul and heart all rolled into one. Typically it controls everything in the dungeon. Expanding the chambers and passages, decorating the environment, creating the monsters and loot, consuming the mana, life force, souls, or what have you, of adventurers who explore and/or die within its territory, subsuming the power for their own use in a never-ending cycle of growth and creation. A Dungeon Core is almost like a Dungeon Master in D&D. They build the environment and encounters and so on for adventurers to challenge. They can of course have other functions, for instance in cultivation stories, few things can draw in and purify as much essence as a Dungeon Core, and they can basically function as cultivation sources for other creatures.