Sunken Mansion

The Sunken Mansion would be like the Woodland Mansion with some key changes.

It would generate in Swamps, and partially in the ground, flooding the Mansion with water, and dirt. It would add a big item to explore swamps for, but wouldn't make Witch Huts any less appealing to find. 

The Sunken Mansion could generate with new blocks like mud and mossy wood. It's loot table would mostly be the same, but include more rotten foods and suspicious stews.