Epidermal Petrification

You touch a willing creature, and the outermost layers of its skin become like rock. If the creature is unwilling, you must make a melee spell attack, and they may make a constitution saving throw to make the spell fail. Upon success, this spell has different effects based on the willingness of the target.

Willing: The target gains 15 temporary hit points, as well as resistance to piercing and slashing damage from weapons that do not have the heavy tag. The target also gains vulnerability to bludgeoning damage and any damage done by heavy melee weapons. If they lose the hit points gained by this spell, the spell ends. If the last hit points gained by this spell are removed by damage the target is vulnerable to, or a critical hit, they gain vulnerability to bludgeoning, piercing and slashing damage for one minute. If this spell is cast on the same target while they have this vulnerability, the spell automatically fails.

Unwilling: The target gains 15 temporary hit points, as well as resistance to piercing and slashing damage from all weapons that aren't heavy melee. The target also gains vulnerability to bludgeoning damage and any damage done by heavy melee weapons. If they lose the hit points gained by this spell, the spell ends. While the spell is active, at the start of each of the target's turns, they must make a strength saving throw. If they fail, their movement is halved, attacks against them are made with advantage, all strength or dexterity related checks they make are made with disadvantage, and all attacks they make are made with disadvantage until the start of their next turn. If they fail by (4+the caster's proficiency bonus) or more, they are paralyzed until the spell ends. While paralyzed in this way, they can make a strength saving throw at disadvantage to end the spell entirely. If the last hit points gained by this spell are removed by damage the target is vulnerable to, a critical hit, or the shatter spell, they gain vulnerability to bludgeoning, piercing and slashing damage for one minute. If this spell is cast on the same target while they have this vulnerability, the spell automatically fails.