Greater Creeping Cold

Description
This spell is the same as Creeping Cold, but the duration increases by 1 round, during which the subject takes 4d6 points of cold damage. If you are at least 15th level the spell lasts for 5 rounds and deals 5d6 points of cold damage. If you are at least 20th level, the spell lasts for 6 rounds and deals 6d6 points of cold damage.