A Snow Goon is a hostile, living snowman. They appeared in a single story arc (12/31 1990 to 1/19 1991)
This series began as an attempt by Calvin to bestow life on a snowman by invoking the "great and terrible snow demons." The attempt went wrong and instead of the snowman slave, servant, or butler he set out to create, Calvin got a growling, lurching, hostile monstrosity which he described to Hobbes as a "deranged mutant killer monster snow goon" (The phrase was used as the basis of the title of the Attack of the Deranged Mutant Killer Monster Snow Goons printed collection). The goon went on to create others of its kind; at least one had two heads. Calvin and Hobbes finally killed them by spraying them with the hose while they were sleeping around his house. He made a sign sometime later stating that 40-something snowmen met "a gruesome fate" on the spot of Calvin's house. However, this is probably unlikely, as the strip in which the sign appeared came before the story arc.