New multi-biome Mob idea the "Hoarder"

I think this follows all the rules and expectations for a new mob idea:

The "Hoarder" - A fantasy creature of relatively large size but not necessarily harder to kill than the warden. A mid-game boss since it could be run into before going into the nether, and wouldn't have the same warning of the deep dark biome. Unless if it spawns in cave systems perhaps a new "scratched stone" block starts showing up on exposed surfaces in the area.

I think a "Hoarder's den" should be able spawn in any biome with the y value dependent on the style of hoarder eventually chosen. The design and lore could be based on dragons, basilisks, magpies and sphynxes. Meaning it could eventually vary between being passive and willing to trade unless its riches are bothered to being hostile on sight. I love the idea of it being a semi-passive mob with some sort of trading mechanic.

Depending on the design of the "Hoarder" and if it ends up having hands and thought of some sort, it could have chests and a "gilded cave". If it is more bestial, perhaps some raw packed gold and iron in the walls, and perhaps adding a "sticky diamond block" based on diamonds and slimeballs in a TNT crafting formation, or just a new packed diamond block?

In terms of other mechanics I wonder if it could become aggressive towards players mining in a certain radius of their cave, perhaps bellowing louder and louder as it mines towards the player until both meet or player leaves?

Thanks for your consideration and any votes!