Snowball is Cosmo's pet Hydra (three-headed Dragon) that has been accidentally summoned on numerous occasions to cause chaos and destruction.
Snowball is a gigantic, red three-headed dragon with strong wings, sharp claws, and the ability to breathe fire. He seems to be rather violent and bloodthirsty, but he may be rather peaceful around Cosmo since Cosmo is the only fairy who did not fear him; instead, he happily greets the dragon and hugs it.
Snowball is first revealed to exist in This is Your Wish when Cosmo's childhood is shown. While the students were playing sports, they turned hockey pucks into beautiful butterflies or peaceful birds. On the other hand, Cosmo turned it into Snowball, and while the other kids were screaming with fear, Cosmo merely cried out happily, "It's Snowball!"
Snowball was seen again when Cosmo was sent to the Fairy Academy. While performing in front of several other officers, Cosmo accidentally turned a nearby bird into Snowball, who promptly breathed fire onto Jorgen and the officers, making Jorgen lose one of his five stars.