Meowstic's appearance differs drastically between genders, but in either form, it is a bipedal feline Pokémon with a humanlike posture, digitless appendages, and two tails. The male's fur is predominantly dark blue with accentuations of white, while the female's color scheme is reversed. The male's ears are mostly blue with some accents of white, and the tips are pointed straight; the female's ears are entirely white, and the tips are curled. The tuft of fur between the male's ears is white and in a straight, diagonal style; the female's tuft is blue and curled. The collar of fur around the male's neck is white and in a pointy style, while the female's collar is blue with a curl rising up to its face. The male's eyes are spring green with darker green pupils, while the female's eyes are yellow with red pupils. The male's tails each have a white stripe just before ending in white, while the tails themselves end in a point; the female's tails are blue at the base and end in white fluffy curls. The male's arms end in white, and its legs are white at foot level; the female's arms end in blue, and its legs are mostly blue in a fashion resembling stockings.
The organs hidden in Meowstic's ears emit psychic energy powerful enough to obliterate a 10-ton truck. It usually keeps its ears tightly shut in order to keep its otherwise uncontrollable power in check, but it will unleash this power if threatened. It usually keeps a stoic, virtually emotionless face; some Trainers adore its unsociable demeanor. The moves it naturally learns depend on its gender; the male's learnset includes mostly supportive and disruptive moves, while the female's focuses on all-out offense.
Meowstic is the only Pokémon to have separate movesets for each gender.
During Google's April Fools' Day 2014 event, Meowstic's genders had separate Dex numbers in Google's regional Dex. The male was #139, while the female was #140.
Meowstic may be based on the domesticated variety of nekomata, a cat yōkai that comes from a domesticated cat who lives many years until its tail splits and it gains supernatural powers, much like how Meowstic evolves from Espurr. Nekomata were often depicted as standing on two legs like a human, and in at least one account shown to be wearing handkerchiefs on their heads, similar to Meowstic.
It could also be based on the very similar bakeneko. In addition, its folded ears are similar to the Scottish Fold breed of cat.
Meowstic is a combination of meow and mystic. It may also derive from stoic, referring to its generally emotionless facial expression.
Nyaonix may be a combination of ニャー nyā or ニャーオ nyāo (meow) and onyx or ὄνυξ ónyx (Greek for claw), psionics, or the Greek goddess Nyx (goddess of the night, associated with magic).