Use Fighting type attacks
Slaking: A normal type which is heavy and sleepy. The perfect match would be Primeape. Primeape has an ability which enables it to stay awake when its foe tries to make it sleep. Since Slaking usually knows Yawn, this is a good advantage. Primeape is also a fighting type which would be super-effective against Slaking. Also, if you teach it Low Kick- which is more effective on heavier pokemon- you have a winning stratedgy against Slaking. Just make sure it has a high enough level.
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
Slaking: A normal type which is heavy and sleepy. The perfect match would be Primeape. Primeape has an ability which enables it to stay awake when its foe tries to make it sleep. Since Slaking usually knows Yawn, this is a good advantage. Primeape is also a fighting type which would be super-effective against Slaking. Also, if you teach it Low Kick- which is more effective on heavier pokemon- you have a winning stratedgy against Slaking. Just make sure it has a high enough level.
Slaking is weak against Fighting-type moves.
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.
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.
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.