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. Once wrapped around its prey, it never lets go. It eats the prey by tearing at it with sharp fangs. Its tentacles are highly developed as if they are hands and feet. As soon as it ensnares prey, it bites.
Pokédex entry #139
omastar in Pokémon GO
It's possible to hatch omastar from an egg?
No, omastar can't be hatched.
Which are omastar’s strengths and weaknesses?
omastar is a rock and water type Pokémon. rock type pokémons are strong against fire, flying, bug pokémons but weak against water, grass pokémons. water type pokémons are strong against fire, ground, rock pokémons but weak against water, grass, dragon, electric pokémons.