Avilio's Intensify Wounds

You choose up to five targets. Each one must be missing hit points. If you try to cast this spell on a creature with full hit points, the spell fails and you take 14d6 psychic damage. Each creature must succeed on a constitution saving throw or take 15d8 necrotic damage as their wounds grow longer, deeper, and deadlier. They must then succeed on another constitution saving throw or have their hit point maximum decreased so that it is equal to their current hit points. Any creature affected by this spell cannot be healed or resurrected by anything short of a Wish spell.