* Bug: Bug-type attacks are super effective against Psychic-types.
* Ghost: Ghost-type attacks are super effective against Psychic-types.
* Dark: Dark-type attacks are super effective against Psychic-types.
Here are some specific Pokemon you can use in Diamond that are strong against Psychic-types:
* Gengar: A powerful Ghost/Poison type with access to strong Ghost and Dark moves.
* Houndoom: A strong Dark/Fire type with powerful Dark moves.
* Sableye: A Dark/Ghost type with access to some good Ghost and Dark moves.
* Pinsir: A powerful Bug-type with strong Bug moves.
* Heracross: Another powerful Bug-type with good Bug and Fighting moves.
Important Notes:
* Psychic types are resistant to Fighting moves, so avoid using those against them.
* Some Psychic-type Pokemon might know moves that are super effective against Bug, Ghost, or Dark-types, so be aware of their movepool.
* Consider using Pokemon with moves that can bypass types, like "Shadow Sneak" or "Extreme Speed."
Good luck battling those Psychic-types!