Black Ice

Select a 5ft cube of ice. Create a 20ft radius circle of Black Ice, which is difficult terrain. If a creature starts or ends its turn on Black Ice, it takes 3d10 Necrotic damage. If a creature falls prone on Black Ice, it takes 3d10 Necrotic damage. As a bonus action, the caster may enforce a Constitution saving throw on all creatures standing on Black Ice. On fail, they take 3d10 cold damage, and have their speed reduced to 0ft. They take only half damage on success. Once concentration or duration ends, Black Ice simply becomes difficult icy terrain, melted by adjacent fire damage.