Encase yourself in an impenetrable tomb made from slabs of translucent ice fixed to the ground. You are protected as if with an otiluke’s resilient sphere spell, but you cannot move or be moved. A spherical zone of permafrost and frigid winds, with a radius of 30 feet, emanates from you and spreads around corners. All creatures in the zone must succeed a Constitution saving throw or receive 12d8 Cold damage and become Frozen, regardless of how many dice of Cold damage it receives. Those that succeed receive half damage.
While in this zone, all creatures have their movement speed halved and all Frozen creatures will not be unfrozen when they receive damage. On each of your turns, you must use an action to maintain this spell or it ends. Each time you use this action, the zone’s radius increases by 15 feet and and the initial cast repeats, requiring all creatures in the zone to make another saving throw and renewing their Frozen condition should they fail.
You can end this spell with a bonus action. The damage roll of the first and subsequent casts is increased by 1d8 per hit-die you were missing when you first cast this spell (after spending hit-dice on this spell). In the initial cast, you can select up to 5 creatures you can see to be immune to all effects of this spell, spending 1 hit-die for each.