Like any other Water type, Gastodon is extremely weak to Grass types like Torterra or Roserade. However, since Gastrodon is also part Ground type, it is resistant to Electric types, such as Raichu.
So when you face a much-stronger-than-you Gastrodon, let loose on the Giga Drains.
Ghost & Flying. I believe that's it! Not dark or bug because although they're super-effective against Psychic, they are not-effective against Fighting. And not Psychic, because though it's super-effective against Fighting, it's not-effective against Psychic.
Water and Grass attacks are super effective against Onix.
psychic pokemons and attacks are super effective
super effective is bug
Rock, electric, ice, and psychic types are super effective against Crobat.
Flying and Psychic are super effective against fighting
Lightning is super effective against water. I hope this helps.
Ghost & Flying. I believe that's it! Not dark or bug because although they're super-effective against Psychic, they are not-effective against Fighting. And not Psychic, because though it's super-effective against Fighting, it's not-effective against Psychic.
Water and Grass attacks are super effective against Onix.
super effective is bug
psychic pokemons and attacks are super effective
Bug Type and Fighting Type moves are super effective against it.
Steel is super effective against rock type pokemon.
Rock, electric, ice, and psychic types are super effective against Crobat.
normal type Pokemon are not super effective against any type.
Bug types are super effective against Dark, Grass and Psychic (x2) in Generation II-onward. In Generation I, they were super effective against Grass, Poison and Psychic.
Actually the Ground is the only super effective type against thunder type pokemon.