Once Gyarados goes on a rampage, its ferociously violent blood doesn’t calm until it has burned everything down. There are records of this Pokémon’s rampages lasting a whole month. Rarely seen in the wild. Huge and vicious, it is capable of destroying entire cities in a rage. In ancient literature, there is a record of a Gyarados that razed a village when violence flared.
Pokédex entry #130
gyarados in Pokémon GO
It's possible to hatch gyarados from an egg?
No, gyarados can't be hatched.
Which are gyarados’s strengths and weaknesses?
gyarados is a flying and water type Pokémon. flying type pokémons are strong against grass, fighting, bug pokémons but weak against electric, rock pokémons. water type pokémons are strong against fire, ground, rock pokémons but weak against water, grass, dragon, electric pokémons.