Frosty is a droid sent by Bertie to take over a crystal point in Tokyo. She has a blue gem on her forehead and she can freeze people with her breath. She appeared in Sailor Moon R Episode 16, Sailor Mercury Moving On?
Frosty opened an ice cream shop located on a crystal point, where anyone who are her ice cream would fall under her spell, where she would freeze them. When Artemis discovered this, Bertie and Frosty discovered him, and Frosty froze him. Sailor Venus and Luna came to stop her, but Frosty froze Luna as well. Sailor Moon, Sailor Mars, and Sailor Jupiter also arrived at the scene to fight Frosty, but she nearly froze them all, until Sailor Mercury (who was going to Germany to study to become a doctor, but decided against it at the last minute) arrived and hit Frosty with her new attack, Shine Aqua Illusion, and Sailor Moon destroyed her with her scepter.
Her name, obviously, comes from the fact that her element is ice.