Litten is a quadrupedal, feline Pokémon covered with primarily black fur. It has a short muzzle with a tiny, black nose, red eyes with yellow sclerae, and short, pointed ears with pale gray insides. There are two red stripes around each of its legs and two horizontal stripes with a vertical stripe across them on its forehead. The lower part of Litten's face is also red, and there is a large tuft of fur on each cheek. A tuft of fur sits at the end of its long tail. When it arches its back, three pointed tufts of fur with red tips appear along its spine.
Litten is a solitary Pokémon that does not typically display its emotions, and it is usually advised that it not be given too much affection. It will scratch those who try to pet it without earning its trust, which takes some time to develop. While grooming, Litten collects fur inside its stomach. By setting the stored fur alight, it can spit fireballs that change based on how it coughs. Litten's fur produces flammable oils, and when it begins shedding, it burns all its fur in a blaze. Its fur coat regrows twice a year.
Litten's Japanese name and its romanization were revealed in a tweet of their trademark on March 27, 2016.
Litten may be based on mackerel tabbies, due to the stripes on its legs and the marking on its forehead, and black cats. Mackerel tabbies are also called "tiger cats" and Litten's coloration may be based off tigers. The combination of its forehead markings and its eyes appears to form one of the alchemical symbols for sulfur, a highly-flammable chemical.
Litten may be a combination of lit, little, and kitten.
Nyabby may be a combination of ニャー nyā (meow), tabby, and 火 hi (fire).