The defensive capabilities of Psychic-types are generally poor. The only types resisted by them are Fighting and themselves, while carrying weaknesses to Ghost as well as the extremely common Dark and Bug. Psychic-type Pokémon often fall to a single strong Dark-type move, such as Crunch, due to the high Attack stat of many Dark-type Pokémon versus the typically low Defense and HP of Psychic-types. In addition, the low Defense many Psychics have frequently makes their Fighting resistance ineffective. Prior to Generation VI, Steel/Psychic types were exempt from these weaknesses due to their typing, but since Dark and Ghost are no longer resisted by Steel, this is no longer the case.
Most Psychic types have a high Special Defense stat, as well as outliers with high Defense and HP stats, such as Lugia and Cresselia. Psychic-type moves tend to have supporting effects, such as Reflect, Light Screen, Skill Swap, and Trick Room, which benefit both themselves and their teammates, giving them greater utility and survivability.
Psychic-type Pokémon and moves have been very popular since Generation I due to their typically high Special Attack and being resisted by only two types, including themselves. They are super-effective against Fighting and Poison types, the latter of which is otherwise strong defensively and the former of which tend to have low Special Defense.
The biggest drawback of Psychic-type moves is that they do not affect Dark-type Pokémon, although this weakness can be removed with Miracle Eye. However, this is not always necessary as many Psychic-type Pokémon can learn moves super-effective against Dark types, such as strong Fighting type moves like Focus Blast, and Dazzling Gleam, a powerful Fairy-type move. Psychics also have access to a wide range of special moves from nearly every type, which can make their Ghost and Bug weaknesses ineffective.
When used in Contests, Psychic-type moves are typically Clever moves, but can also be of the other four Contest types, excluding Tough.
Generation I Balance issues
Psychic-type Pokémon were at the center of a balance issue in the Generation I games. The issue arose from the lack of an effective countermeasure against Psychic types caused by the absence of any powerful Bug-type moves (at the time the only weakness of Psychic types). Strengthening the gap was the fact that the only Bug-type Pokémon to know the only potentially good Bug moves — Beedrill with its Twineedle and Pin Missile — was also part Poison-type, creating a vulnerability to Psychic moves, and that in the first-generation games, Ghost-type moves were not only ineffective against Psychic Pokémon, but the only Ghost Pokémon at the time were part-Poison, also creating a vulnerability, not to mention the fact that the only Ghost-type move that would be affected by type matchups at the time was exceedingly weak. Also, Poison-type Pokémon were fairly common in Generation I, and the only type to resist Psychic-type moves was the Psychic type itself, meaning a weakness to the type was common in itself.
The issue was rectified in later generations with the addition of Steel and Dark types, an added weakness to Ghost-type moves, and more powerful Bug- and Ghost-type moves.
As of Generation VII, there are 85 Psychic-type Pokémon or 10.5% of all Pokémon (counting those that are Psychic-type in at least one of their forms, including Alola Forms), making it the 5th most common type.
Due to the decreased amount of types in the TCG, Psychic generally adopts all Ghost-type Pokémon under its typing. It also adopted Poison-type Pokémon after the Diamond & Pearl set, whereas previously they were a part of the Grass-type.
Similar to the games, Psychic-type Pokémon in the TCG are generally weak to other Psychic Pokémon, with no resistances. Psychic-type Pokémon are strong against Grass (until Diamond & Pearl), Fighting and Psychic Pokémon, whilst Colorless, Darkness and Metal Pokémon can resist this type.
Generation III introduced the most Psychic-type Pokémon of any generation, with 20, and Generation VI introduced the fewest Psychic-type Pokémon, with six.
Generation I introduced the most Psychic-type moves of any generation, with 15, and Generation VI introduced the fewest Psychic-type moves with only one.
Psychic is the most common type for Legendary and Mythical Pokémon, with at least two Psychic-type Legendary or Mythical Pokémon introduced in each generation (except Generation VI, which has only introduced one) for a total of 19 (out of 71).
The Psychic type is the only former special type to not have any of its old moves changed into physical moves, while the Fighting type is the only former physical type to not have any of its old moves changed into special moves.
Counter and Mirror Coat, moves countering physical and special attacks are, respectively, Fighting- and Psychic-type moves.
Bulk Up and Calm Mind, moves raising physical and special stats are, respectively, Fighting- and Psychic-type moves.
A Pokémon cannot have a double resistance to Psychic without being a Psychic type itself.
However, a Psychic-type Pokémon also cannot have a double resistance to more than one type.
↑ Sugimori, Ken "Psychic Pokémon seemed to dominate in the previous Pokémon game, so we needed to come up with new Pokémon and types to make Gold and Silver more balanced." Nintendo Power 134 (July 2000) p. 79 (retrieved August 16, 2010)