Cage of Bones

You choose a creature within range. It must succeed on a Dexterity saving throw or is caged inside shifting spiked bones that pierce its body. While caged, the target is restrained and takes 2d4 piercing damage at the end of each of its turns.

The cage can be destroyed. It has AC 15, 40 Hit Points, immunity to poison and psychic damage, and vulnerability to bludgeoning damage.