Nick pets are a special release pet. They were created by Nick, co-owner, and coder of the site. While Nick's coding skills are great, his drawing skills are slightly lacking. Many comment that the pets look like they were drawn by a little kid, but, most Nick Pet fans consider that part of their charm, though, not everyone enjoys these pets. But there is a significant enough population on CS that loves them enough to make them highly popular.
Most of the Nick pets are worth a Malk pet.