"Omastar uses its tentacles to capture its prey. It is believed to have become extinct because its shell grew too large and heavy, causing its movements to become too slow and ponderous."
If Omantye was meant to be a cute fossil Pokemon, then Omastar is one that proves you get more intimidating as you evolve. Just the look of Omastar shows that it's a powerful Pokemon, and if used correctly, can be a very big asset for your time.
Omastar's Basic Attacks are Water Gun and Mud Shot, while its Special Attack is Brine.