Brilliant Frost Nova

Through great arcane strain, you summon the true potential of ice magic. Channeling your magic into the ice used in this spell, you create a 6 inch diameter orb of pure ice magic, which you then hurl at a point within range. All creatures within a 100 feet radius of the point that the ice orb landed that you designate when you cast the spell at must make a Dexterity saving throw against your spell save DC. Creatures that fail the saving throw take 40d12 cold damage, and become entombed in magic ice. Creatures that pass the saving throw take half damage and don't become entombed in magic ice. Creatures that you don't designate automatically pass the save and don't take any damage. 

Each instance of magic ice has an AC of 15, cannot be damaged by any damage type other than magic bludgeoning or fire from a magic source, and has 25hp if it has entombed a tiny creature, 50hp for small and medium creatures, 100hp for large creatures, 150hp for huge creatures, and 200hp for gargantuan creatures. Each instance is separate per creature, and as such, shattering or melting the ice for one creature doesn't shatter another creature's instance, even if the instance was in contact with another instance. Spells that were being cast by a creature during this spell's effect also become entombed with the creature, but doesn't break their concentration, allowing the creature to maintain concentration on certain spells (I.E. Banishment for a Devil). Creatures that die from this damage become as fragile as the ice, with the shattering of the ice also shattering the creature's corpse. This magic ice can also be used as the material component for "Brilliant Frost Nova." Casting a spell such as "Dispel Magic" on an instance renders the ice as normal ice, which allows it to be broken by other means other than magical fire and magic bludgeoning.

If an instance of magic ice is left unbroken, that instance will last forever, preserving the creature inside until something or someone breaks the ice and sets the creature free. Any creature entombed in the ice cannot break out of it themselves unless they kept consciousness while entombed. Any attempt of smashing the ice from inside out will require a strength save, using your spell save DC as the DC required to break the ice. If the entombed creature is made of fire, is gargantuan in size, or has at least a 24 in strength, they have advantage on this save. This save can be repeated once per round.