Bone Cocoon

You conjure a cocoon made of cartilage and bones, which protects the creature that dropped to 0 hit points. While in the cocoon, the creature can’t be damaged by attacks or effects originating from outside, has total cover, is considered restrained, and makes death-saving throws at advantage.

The cocoon has 25 hit points and an AC of 11 + your spellcasting ability modifier. It has resistance to cold, fire, and necrotic damage, and immunity to poison and psychic damage. If you lose concentration or the cocoon is reduced to 0 hit points, it is destroyed.