Omastar

Omastar, the second evolutionary stage for Omanyte, is a prehistoric Pokemon that became extinct when it's heavy shell made it impossible to catch prey. In "Attack of the Prehistoric Pokemon" Ash and friends engage in a Pokemon fossil hunt. As Ash digs deeper into the canyon floor, the ground falls in beneath him. He plummets into an underground cave and finds himself surrounded by legions of extinct Omastar and Omanyte!

First appearance: Episode 46 — "Attack of the Prehistoric Pokemon"