There are 5 cats and are all different colors, such as blue, magenta, calico, green, and black, all colors of the Maneki-neko, which is also what the Lucky Cat Mario is based off of. There is a rumor that says the cats are represent the cat versions of the characters, green for Luigi, pink for Peach, blue for Toad and black for Rosalina (in her cat form). The Cats are usually friendly and caress Cat Mario, relax or groom themselves. Mario can pick up an individual Cat and it will scratch things in front of it like enemies and other things. When Mario is near a Cat and wearing a cat suit, it will dash towards Mario and rub up against him. Otherwise, the cats will run away from him.
The Cat's look more evil-like when Fury Bowser is around. They all turn black with red eyes and spiky fur, and they will hurt Mario when nearby. Evil cats can be big, medium, or small. To tell when Fury Bowser is going to appear it will start raining.
Cats are implemented as a mechanic for obtaining three different Cat Shines. Mario can find a larger calico cat near each of the three Giga Bells crying. Once approached, a bubble will appear over the cat's head requesting Mario to find their lost kittens, who are also calico cats. When Mario brings back all of the kittens, he will obtain the Cat Shine. Each Cat Shine using this format can only be obtained if Mario did the previous Cat Shine. The more levels you unlock, the harder the cat's hide.
The cats appear as spirits under the name "Kittens". They can be obtained on the spirit board over a limited time.