Before Generation VI, the Dragon-type was perhaps the most overpowered type in the Pokémon series. Steel was the only type that resisted it, leaving Dragon relatively unchecked offensively. When Fairy entered the franchise, though, it dramatically disrupted the meta. Fairy is one of the least prevalent types, but several Pokémon have only this typing, including some that gained it retroactively.
Some of these Pocket Monsters are underwhelming, but others are useful in the main series games. As the best counter to the Dragon-type, Fairy plays an important role in the series. Trainers should consider using some of the strongest pure Fairy-type Pokémon when they are available.
Slurpuff
Generation VI's Slurpuff lives in relative obscurity, forgotten by a large portion of the Pokémon fanbase. This is partially due to its design, which some find off-putting. Regardless of its aesthetic, it is one of Pokémon's most underrated Fairy-types because despite what many think, it can be somewhat capable in battle.
Surpuff is nothing extraordinary, with consistent stats that are all only decent. However, it is stronger than many players realize, especially when trainers are early in their journeys. Its Speed is mediocre, but it is often good enough to out-speed opponents in early-game portions. It also has a reasonable move pool that allows for some coverage options. Slurpuff may not be great, but it is not as useless as some fans may assume.
Comfey
With a very low HP stat, Comfey may initially appear too weak to properly compete. However, its Defense is reasonable and its Special Defense is high, partially making up for this deficit. Comfey is also faster than many Pokémon, but its offensive stats are not high enough to consistently knock enemies out in one turn. Its Special Attack is better than its Physical side, but it is still not exceptional.
Access to a few powerful Special attacks gives this stat more utility, although only one of these moves has the Fairy typing. The other moves do not gain a Same-type Attack Bonus, but they can provide some additional coverage.
Granbull
Granbull entered the series in Generation II as a Normal-type but then became a Fairy-type in Generation VI. Its low Special Attack limits it to the Physical side, but it has a great Attack stat, allowing it to specialize very well in Physical strikes. Oddly, Granbull only learns one Fairy attack through leveling up: Play Rough. This move is very powerful, but the rest of its attacks do not gain the same bonus this one does.
Nevertheless, its other moves provide excellent coverage and use its high Attack stat. Unfortunately, the Pokémon is rather slow, and while its defensive stats and HP can usually take a hit or two, it gets worn down fairly quickly.
Clefable
Like Granbull, Clefable was initially a Normal-type, which changed in Generation VI. This Pokémon has an interesting move pool, in that most of its accessible actions are in the Status category. Several of these are healing moves, and since Clefable is quite bulky, this helps it significantly. Opponents often have to wear it down to defeat it, and these moves can undo that damage completely.
On the offensive side, Clefable has an above-average Special Attack stat, but not many Special moves without the use of TMs or TRs. Its Speed is mediocre, but attacking quickly is not Clefable's focus.
Alcremie
A Pokémon with an absurd number of alternate forms and a Gigantamax variant, Alcremie is unique in the Pokémon world. Not only is this pure Fairy-type cute, but it can also hold its own in Special matchups. Both stats of this category are high, with its Special Defense being quite impressive.
In many other types of battles, though, Alcremie falls short. Both of its Physical stats are underwhelming, but its Defense is slightly higher. Its HP is also low, so it has no bulk when facing Physical specialists. In these situations, acting first can benefit it, but its Speed stat is too low to do so consistently.
Aromatisse
As the counterpart to Slurpuff, Aromatisse is also somewhat divisive among fans, leading it to be less known than many other Fairy-types. Unlike Slurpuff, Aromatisse's stat spread allows it to specialize more. In this case, it helps the Pokémon greatly. Its Speed is almost nonexistent, but its HP and defensive stats are more capable of dealing with damage than those of its counterpart.
Its Special Attack is fairly high, which allows it to use some of the most powerful Fairy moves like Draining Kiss and Moonblast to great effect. While its stat spread is good, its base stat total is not high enough to compete with more powerful Fairy-types. All in all, Aromatisse is not extraordinary, but it is stronger than it is given credit for.
Sylveon
As the Fairy Eeveelution, Sylveon embraces the Special nature that often accompanies this type. Its Special Defense is its highest stat, and its Special Attack is not very far behind. It does not have access to great coverage moves from leveling up, but it can learn some great Fairy attacks.
Its Physical stats are lacking, which can be a bit of a problem when facing Physical attackers, but Sylveon's HP is high enough to soften the blows. Despite this, Sylveon is most comfortable against Special attackers, especially since its mediocre Speed stat only sometimes allows it to act first.
Florges
Like Sylveon, Florges excels when facing Special attackers. Its Special Defense stat is huge, but its Defense is unimpressive. It is not exceptionally quick, but Florges is fast enough to out-speed many opponents that may try to take advantage of its low Defense.
An underwhelming Attack stat limits it to mostly using Special strikes, and this stat is much higher. Although limited in its coverage options, its move pool has a few great Fairy and Grass attacks. While it has its weaknesses, Florges can be dominant in the Special department.
Zacian (Hero of Many Battles)
Although its Crowned Sword form is stronger and makes it one of the best dual-type Fairy Pokémon in the series, Zacian's Hero of Many Battles form is also quite powerful. Without the Rusted Sword, Zacian is a pure Fairy-type, and like its stronger variation, it focuses on fast strikes with its high Attack stat. Zacian's Ability Intrepid Sword further boosts this stat when it enters the battle.
With high defensive stats and reasonable HP, Zacian is not easy to take down, either. Its only downside is its much lower Special Attack, but even this stat is not terrible. As the box art Legendary for Pokémon Sword, Zacian does not disappoint.
Xerneas
While it is not as fast as Zacian, Xerneas has amazing offensive capabilities. Both its Special and Physical Attack have the same stat value, giving Xerneas more options than Zacian has. It has a reasonable Speed, but even if it cannot move faster than its opponent, it can easily survive most strikes with the combination of its good defensive stats and its excellent HP.
Its signature move, Geomancy, significantly raises its Special stats and Speed. While this move takes two turns to use, Xerneas can almost always survive long enough to make use of it. It is the box art Legendary of Pokémon X, and its battling capabilities show why.