Devil's Snare

You imprison a Huge or smaller creature within a large pillar of foul, abnormally cold ice that completely encases it and begins rapidly atrophying it's entire body. The creature must make a CON saving throw or take 8d10 cold damage on a failed save or half damage upon success. This spell ignores resistance to cold damage and treats immunity to cold damage as resistance to cold damage instead. If the creature survives, it's imprisoned within the pillar of ice and therefore: restrained, has immunity to fire, cold, and poison damage, and has resistance to all other forms of damage for the spell's duration as long as you maintain concentration. The pillar of ice has an AC equal to your spell save DC and can be shattered from the outside, (releasing the target), if it takes more than 150 damage. An imprisoned creature can also make a STR check with a DC equal to your spell save DC at the start of each of its turns while imprisoned to break out. At the start of each of the creatures's turns while imprisoned, it must make a CON saving throw to resist the atrophic effects of the ice. If the creature fails a CON save while imprisoned, it gains 2 levels of exhaustion. After three failures on CON saves while imprisoned, it dies, as the unnaturally destructive properties of the ice have now completely destroyed it's physical body. If a creature dies in this manner or is killed by the initial cold damage, it suffers the effects of a Soul Cage spell as the ice ensnares it's soul once it's body is gone. 

 At Higher Levels. At 9th level, if a creature has more than 100 hit points while imprisoned, the spell functions as normal. If a creature has 100 hit points or less at any point while imprisoned, it automatically dies and it's soul is trapped within the ice.