Encrustation of Crustaceans

This spell creates a horde of stinging, biting crabs on an enemy. Choose a creature within range. That creature must make a Dexterity saving throw. On a failure, multiple crabs grab onto the target and begin to destroy... At the start of each of it's turns after failing the initial saving throw that creature takes 5 bludgeoning, piercing, and slashing damage and has disadvantage on all Dexterity, Strength and Constitution saving throws and attack rolls made during its turn. The creature must make a Constitution saving throw when it casts a spell with a somatic component - on a failure the spell fails, wasting the spell slot as crabs obstruct the delicate hand gestures required. The crabs, once attached are hard to remove. They can be removed by the target or an adjacent creature succeeding on a Strength (Athletics) or Dexterity (Acrobatics) check, using their action, any AOE effect that deals two or more damage to the square the creature is in, or any spell (such as telekinesis or earthquake) that is capable of removing objects from the target. The crabs can be attacked (AC 12, 25 HP). Each five hit points of damage done to the crabs reduces the damage of the spell by 1 bludgeoning, piercing, and slashing damage.

A creature reduced to zero hit points by this spell is devoured by the crabs, leaving only a hollow cocoon of crabbiness behind.