The catacombs...

The catacombs would be a structure spawning under villages. A new type of house would have the spiral stairs, leading to the catacombs. Laced with skeleton heads, and old, broken, mossy brick walls with hidden pathways to olden treasures and good loot dating back when they were still building the villages.

In order to find the catacombs you would need to find a village, any type wether its a abandoned village or a lively one. You would need to find the cartographer villager house or villager. There would be a chance that you find an old map. Inside it are the location of the catacombs. Note that only 5% of villages only have the catacombs and the map will lead you to a village containing the catacombs, so it may be far away

My idea is that it is like a trial chamber but it only spawns deep underneath villages. Old, musty, and reeks of skeletons. And they would get the "lost" debuff making so they dont know they're sense of direction. implementing it would be hard but i have some ideas, such as making their controls inverted, random, and when they walk forwards, for example, they go left. 

The loot would be like dungeons, but it would have no spawners and skeletons would jump out of nowhere. Scaring you. And hordes of bowless skeletons would swarm you.

A new type of skeletons would appear here such as

tank skeleton. Would be slower but have more health and do more damage

Fast skeleton. Would run faster but deal less damage.

Army skeleton. Would have muskets and deal lots of damage.

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