Pidgeotto is a Normal-Flying type, and as such, it is weak to Rock, Electric, and Ice moves. (These attacks are super-effective, which means they will do double damage). A Pokemon that is one of those types would make those moves even stronger, so a Rock, Ice, or Electric type Pokemon with a signature same-type move should be the best against it.
Pidgeot is immune to Ground and Ghost moves, and resistant to Bug and Grass. It will take normal damage from Normal, Flying, Fighting, Poison, Steel, Fire, Water, Psychic, Dark, Fairy, and Dragon moves.
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 and Flying types in Pokémon battles.
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
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.
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.
Ground-types are super effective against electric-type Pokémon.