Ore Golem Boss

Since the Cave Update is gonna be pretty big, why not add a boss along with it? It would be summoned kind of like the wither, but with certain underground blocks (not sure which, suggestions please). It would have to be spawned on a rock-type block. When it is forming, you can throw ore blocks at it, which would make it stronger, but give it better drops.

Iron would increase its health, Diamond increase its damage, and Gold would make it faster. Using any of these ores would make it drop more of said ore.

The boss would look like a golem made of stone, diorite and andesite, along with some of the ores you used to fuel it. It could burrow under the ground, and also throw ores at you.

A unique mechanic about this boss it how you damage it. Swords and axes would deal half damage to it. Arrows would bounce off of it (unless they had Piercing). The only way to deal decent damage to it would be to use a pickaxe. Pickaxes would have the same damage and speed as its equivalent sword would do. Efficiency would increase damage, Fortune would act as Looting, and Silk Touch would change its drops as if you used it on those blocks (Diamonds becoming Diamond Ore, etc.).

On death, it would drop a guaranteed 10 iron, 5 gold, and 3 diamonds. These amounts would fluctuate greatly depending on what you use to spawn it. It would also drop 1-3 Stone Hearts.