This magical iron cage is lined with rusted spikes like shark teeth, and it is normally no more than a foot in diameter. It is Tiny, but it expands to fit any creature placed inside it, even when multiple creatures are already inside it. It never becomes larger than it needs to, and it stays small enough to torment its prisoners with discomfort and pain, their limbs hanging helplessly through the bars of the cages. Changes in size do not make it easier to escape, as the bars not only lengthen to contain larger creatures but also multiply to contain smaller ones, duplicating from other bars in a repeating pattern to keep the smallest creatures within the cage.

Creatures can only be placed in the cage if they are incapacitated, and only if the one placing them inside is attuned to the birdcage. If the cage is opened by a creature that is attuned to it, each creature inside the cage becomes paralyzed until the door is closed again.

Notes: Banishment, Container