Onyx Chest

This small square chest is only about a foot large in all dimensions. It is beautifully crafted out of some unknown black material. The chest is gilded with gold trim around the edges and on the top in a cross-like pattern. It feels very solid but only weighs about a pound. In the center of the cross on top of the chest is a small hole, possibly for a key of some kind, but just large enough for a finger to be inserted. The details inside the hole seem to be magically obscured in darkness.

This chest requires blood to be attuned to a single user. To attune to this item a creature must insert a finger (or other appendage small enough) into the hole in the top of the chest, at which point they will feel a sharp pain in said finger and suffer 1 point of damage as the chest extracts a drop of blood.

Once attuned the user may use an action to physically open the chest. Once opened, if empty, the chest expands into a shape defined by the user up to 12 cubic feet. While open, any objects that fit can placed inside the chest until the lid is closed. The chest can only hold up to 300 pounds. Once closed the chest immediately reverts to its original size and any objects contained within are magically compressed and have their weight reduced to 1/10 of their original weight. Once opened again, the chest resumes it's previous size, until all items are removed.