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.
Gallade is weak against Ghost, Flying, and Fairy-type moves. Avoid using Fighting and Rock-type moves as much as possible, for those are its resistances.
Water and Grass attacks are super effective against Onix.
Rock, electric, ice, and psychic types are super effective against Crobat.
Steel is super effective against rock type pokemon.
super effective is bug
Gallade is weak against Ghost, Flying, and Fairy-type moves. Avoid using Fighting and Rock-type moves as much as possible, for those are its resistances.
Flying and Psychic are super effective against fighting
Lightning is super effective against Water and Flying types in Pokémon battles.
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.
Rock, electric, ice, and psychic types are super effective against Crobat.
Steel is super effective against rock type pokemon.
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.
normal type Pokemon are not super effective against any type.
Ground-types are super effective against electric-type Pokémon.