Pokémon's Psychic-type has always been one of the strongest. In Generation I, this was especially true, but it became more balanced as the series continued due to the introduction of the Dark and Steel typings in Generation II. However, the Psychic-type is still present on some powerful Pokémon, and it is the most common type for Legendaries and Mythicals.
While pure Psychic-types can dominate in battle, dual-type Psychic Pokémon can gain additional benefits, though they also must deal with the downsides of their other type. These Pocket Monsters can be exceptional in a playthrough, carrying trainers through tough NPC battles. They can be challenging to obtain and often are only available in the post-game. However, they are viable whenever they are accessible.
Hoopa Unbound
Hoopa Unbound, which is also one of the best dual-type Dark Pokémon, is an offensive powerhouse. Both its Attack and Special Attack are extremely high, and with its access to exceptional attacks like Psychic, Dark Pulse, and its signature move, Hyperspace Fury, Hoopa Unbound can sweep through many teams.
The only problem is that while Hoopa Unbound has a reasonable Speed stat, it does not always act before its opponents. Though its Special Defense is high, its Defense stat is sub-par, leaving it vulnerable to Physical attackers. If it can avoid these, however, Hoopa Unbound can appear unstoppable.
Mega Latias
With boosts to the offensive and defensive stats of its base form, Latias's Mega Evolution makes it even more powerful. Its highest stat is its Special Defense, which turns it into a wall against this category of damage, but it can also take Physical damage more than decently as well. This strength is helpful because Mega Latias is weak to a third of the types in the series.
Despite having capable defensive stats, Mega Latias is also fairly fast, letting it use its fantastic Special Attack before many opponents can act. Its Attack is lower, but it is not useless, making Latias a bit of a jack of all trades that can consistently deal damage and survive strikes.
Shadow Rider Calyrex
On its own, Calyrex does not stand tall compared to the strongest Galar Legendary and Mythical Pokémon. Spectrier, however, is quite capable, and when the two work together in the form of Shadow Rider Calyrex, the result is a dangerous opponent to face. Its Speed stat is extremely high, and its Special Attack stat often allows it to get the job done with one swift blow.
Shadow Rider Calyrex gets a further buff to its Special Attack when it knocks out a Pokémon because of Spectrier's signature Ability Grim Neigh. Its defensive stats are not the most impressive, but they are usually enough to let the Pokémon take a hit or two, though it rarely needs to use them.
Mega Gardevoir
Mega Gardevoir's biggest flaws are its HP and its Defense stat. Both are mediocre and leave the Pokémon vulnerable to being knocked out in one strike. If it can avoid fast Physical attackers, though, Mega Gardevoir can be a destructive force.
Its Speed is high enough to allow it to move before a large portion of the Pokémon it encounters, and its exceptional Special Attack stat is often more than enough to defeat enemies in a single blow. Every attack Gardevoir learns from leveling up is Special, giving it a sizable move pool of Psychic and Fairy attacks. Its Special Defense is also quite high, making up a bit for its unimpressive HP stat.
Solgaleo
As a box art Legendary, Solgaleo has a high base stat total. Its best stats are both its HP and its Attack, giving it more than capable bulk and the ability to deal a significant amount of damage in one hit. Its Speed, while not exceptional, is reasonably high, and its Special Attack stat can be utilized to a decent extent if need be.
As a Psychic/Steel-type, Solgaleo resists half of the types in the Pokémon franchise while being weak to four. Because of this, Solgaleo is a very reliable pick for a defensive Legendary, but it is also one that can be incredible offensively.
Mega Mewtwo X
Mewtwo has always been one of the most powerful Pokémon in the series. When it received two Mega Evolutions in Generation VI, Mewtwo got a further buff. Mega Mewtwo Y is perhaps the strongest pure Psychic-type Pokémon, and the Psychic/Fighting Mega Mewtwo X is very possibly the strongest dual-type Psychic Pokémon. Its HP and defensive stats are reasonable but not exceptional. However, it rarely needs to use them.
Its Attack stat is monstrously high, and with its fantastic Speed stat, Mega Mewtwo X can easily knock out a majority of opponents in one strike. Even though its Special Attack stat is not as impressive, it is still terrifying compared to that of most other Pokémon. Both Mega Evolutions for Mewtwo are tied with Mega Rayquaza for having the highest base stat total for any usable Pokémon.
Lunala
Lunala has the same stat spread as Solgaleo, except for the fact that the values for the Physical and Special categories are switched. As a result, Lunala can take an extensive amount of damage before fainting, and its Special Attack stat gives it the power to devastate enemy teams.
The box art Legendary's typing of Psychic/Ghost is a bit of a double-edged sword, giving it only two type weaknesses, both of which are extreme vulnerabilities. Even with these weaknesses, though, Lunala's bulk often lets it survive a couple of hits. In addition, its signature Ability, Shadow Shield, reduces the strength of attacks against it when it is at full health, further helping it defensively.
Mega Latios
Unlike its counterpart Mega Latias, Mega Latios focuses more on its offensive stats. Its Special Attack stat is massive, and its Physical Attack, while less impressive, is still great. Because of its high Speed stat, Mega Latios can swiftly strike enemies and often defeat them in one hit.
When it needs to defend, Mega Latios does not fall flat either. Its Defense is more than reasonable, and its Special Defense is quite high. Sharing its dual-typing with Mega Latias, Mega Latios also has the same six weaknesses, which can be a bigger problem for the latter, but it can still usually deal with damage fairly well.
Ultra Necrozma
Ultra Necrozma provides one of the most memorable mainline Pokémon game boss fights for a reason. The stronger form of the already powerful Necrozma boasts exceptional Physical and Special Attack stats, letting it utilize both categories to devastating effect, regardless of the opponents' defensive strengths.
With the addition of its high Speed stat, Ultra Necrozma can eliminate many enemies before they have the chance to move. It also gains the benefit of its signature Ability Neuroforce, which buffs Ultra Necrozma's super-effective attacks. The Legendary's bulk is its weakest feature, but even this is more than capable of letting it withstand damage.
Mega Metagross
Mega Metagross has the same two types as Solgaleo and, as such, is also resistant to half of the types in the franchise while being vulnerable to four. In addition to this, Mega Metagross's Special Defense is high but not exceptional, making up a reasonable amount for its only decent HP stat.
On the Physical side, Mega Metagross shines. Its Defense stat is incredible, as is its Attack stat. With great Speed as well, the Pokémon is known to demolish enemy teams with relative ease, making it one of the more sought-after Mega Evolved Pocket Monsters.