Gelatinous Cube/Giant Slime

Giant Slimes based on D&D Gelatinous Cubes, also....Baking soda?

A neutral mob the size of a small house that would wander mines & caves, eating/destroying anything in it's path. It's not hostile, it simply moves & anything caught in it's slime is slowly digested. It's body is so acidic that it can push into stone & slowly create caves.

The slime would have bones, bits of stone, & a treasure chest inside. If you have a special enchanted armor, you can have a set amount of time to go into it & grab the treasure before it starts to eat your armor away.

The slime's body could be harvested to make acid that I'm sure players could think of uses for.

Now for how to kill it or keep it at bay.

Introduce Trona, a substance that would be found mining sandstone. It could be refined into baking soda, which would neutralize the acid in large amounts. Baking Sodium Bicorbonate Blocks as a boarder would make the giant slime avoid the area. Sodium Bicarbonate Arrows or quick-dissolving Sodium Bicarbonate Swords would be the only way to kill them. The baking soda could be used to make an armor enchantment to give you time to try to get a chest from inside a slime without killing it.