Omastar is a cephalopodmolluskPokémon similar to an ammonite or nautilus. Its sky blue body has several tentacles; the tentacles toward the front are shorter and thicker than those in the back. There is a pale yellow, helix spiraled shell on its back. Several sharp spikes line the shell's midsection from the front to about halfway down its back. The shell's rim has two circular indents where Omastar's eyes are visible. Its eyes have yellow sclerae and vertically-slit pupils. It has an oval mouth with a four-sectioned, fang-like beak.
It is believed that Omastar's extinction was a consequence of the increasingly heavy weight of its shell that affected its mobility, including its hunting. Omastar swam the seas in search of prey, including prehistoric Shellder. It attacks only when prey comes near its tentacles. Omastar uses its tentacles to ensnare its prey before biting down with the deadly force of its beak. Its fangs are powerful enough to crush through rocks. With the shell broken, it would suck out the contents. Omastar was in turn preyed upon by Carracosta. Omastar is thought to be a distant ancestor to Octillery.
Omanyte and Omastar, Kabuto and Kabutops. It is believed these Pokémon became extinct tens of thousands of years ago. The detail of their behavior is shrouded in mystery. Though some have speculated that they may still exist, none of these Pokémon have ever been seen alive.
In early English-language promotional material for Pokémon Red and Blue, Omastar was originally known as "Kargo". This name is derived from "escargot" (French for snail).
Omastar appears to be based on a type of ammonite, prehistoric mollusks related to the present-day squid and octopus that lived between the Devonian period and the Cretaceous period.
In addition, its method of grabbing prey and cracking their shells with ring-shaped mouths may be based on Anomalocaris. It may also draw inspiration from the nautilus, a species of modern-day mollusk.
Omastar may be a combination of its Japanese name, a phonetic anagram of ammonite, and star, for its body shape and five-pointed shell.
Omstar may be a combination of 鸚鵡貝 ōmugai (nautilus) and star.