Malk Pets are a catagory of pets that were drawn by the artist Malk. They have a different, somewhat more realistic style from the other pets on CS. Malk draws cat, wolf, dog, fox, horse, spider, owl, koi fish, beta fish, cerberus (3-headed dog), sleipnir (6-legged horse), and dragon linearts. Malk is now retired from CS staff along with most of her lines.
Sleipnirs were released as Chicken Smoothie Store Pets and cost 20C$ each in 2009.
Malk Pets are currently worth more than a normal pet because of their date. You can sometimes adopt Malk Pets if you adopt a pound pet RIGHT when they open. Just look for a unusual animal that you cannot adopt at the adoption center.