Vilmar's Wreathe Flames

You create a wreathe of flames on the floor encircling a creature of your choice and then erupting in a 10ft radius dome of pure flame around them. The creature or creatures in the effected area must make a dexterity saving throw or take 6d6 fire damage and be considered restrained within the sphere. Creatures who succeed take half damage and are not restrained but are moved to a space outside of the sphere's influence. 

Restrained creatures take 2d6 fire damage at the top of their turn and can make a dexterity saving throw to attempt to escape. If they escape through a dexterity saving throw they take half 2d6. 

Creatures may also choose to force their way out, rather than attempting to do so safely. Creatures choosing to do so will take a flat 24 fire damage, but will no longer be considered restrained.

Gargantuan or Huge creatures are unaffected by the restraining effects of Vilmar's Wreathe Flames.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the initial and restrained damage increases by 1d6 for each slot level above 3rd.