Psychic-type Pokemon are weak to Bug, Ghost, and Dark-type Pokemon). Dark-types are especially useful as they are immune to Psychic moves. Psychic moves also don’t do very much damage against Steel Pokemon or other Psychic types. It is important to note that a Psychic-type Pokemon could also have a second type, which means they’ll also be weak against other forms of damage relating to that type. For example, if you were battling the mythical Grass/Psychic-type Celebi, then fire moves would also be effective against it.