Bone Maiden

A target in range must succeed a Charisma saving throw  or be banished inside inside an Iron Maiden formed of bone that appears in its space. They are considered restrained and incapacitated, immune to all damage coming from the outside, and take 3d6 piercing damage at the start of their turn, as spikes of bones dig into their body. At the end of each of their turns a trapped creature can repeat the saving throw, escaping on a success. The bone maiden has AC 14, 80 HP, immunity to psychic & poison damage, and is vulnerable to bludgeoning damage. If the maiden is destroyed the creature inside is freed.