Although the most die-hard of Pokemon fans can probably keep up with the hundreds of Pokemon introduced throughout the past eight generations, more casual fans may need help keeping track of everything. With every new generation comes a host of new legendary Pokemon that each have a unique place in the lore of the Pokemon world, and some players are finding themselves in need of a rundown of what each legendary does and how they affect the world of Pokemon. The first four generations of Pokemon game saw the introduction of 26 legendary Pokemon and nine mythical Pokemon, totaling 35 legendary-like Pokemon in all.
For those unaware, there are two categories of legendary-like Pokemon in Pokemon games. Legendary Pokemon are what they sound like: extremely powerful, usually unique Pokemon which have either a sphere of influence, a greater purpose, or a role in the creation myth of the Pokemon world. Mythical Pokemon, on the other hand, are similar in terms of power and importance, but are even rarer to the point where some scholars in the world of Pokemon doubt their very existence. The distinction in game is that mythical Pokemon cannot usually be acquired through normal means and must be attained via events. For the most part, legendary Pokemon come in pairs or trios and are named in relation to their place in lore.
Generation 1
Legendary Birds - Moltres, Articuno, and Zapdos
Perhaps some of the most recognizable legendary Pokemon are Moltres, Articuno, and Zapdos, the legendary birds. Aside from being some of the first legendary Pokemon ever (they debuted in Pokémon's very first generation), they have made several appearances in movies, anime episodes, games, and the like. More recently, they act as the symbol for the three teams of Pokemon Go. These legendary birds are sometimes associated with seasons, and each has the ability to control the element it is associated with (Moltres controls fire, Articuno controls ice, and Zapdos controls lightning). It seems these may also be the first legendary to receive region-form changes, as Pokemon Sword and Shield's Expansion pass might be adding Galarian Moltres, Articuno, and Zapdos.
Mewtwo and Mew
Mewtwo does not come in a pair or a trio, but is an entity all his own. Mewtwo was created in a lab, using DNA from an ancient Pokemon named Mew, who was thought to be all but extinct. By contrast, Mew is considered a mythical Pokemon, meaning it is so rare that its existence is questionable. Both Mew and, to a greater degree, Mewtwo have incredible psychic and mental abilities, and Mewtwo is thought to be far smarter than most humans, even the ones that created him. Mewtwo originally debuted in the first generation of Pokemon games and was one of, if not the, strongest Pokemon available. Since then, he has appeared in several other generations and is featured prominently in the anime and its movies as an important character.
Generation 2
Legendary Beasts (Entei, Suicune, and Raikou)
In Generation 2, three legendary beasts were added; Entei, Suiciune, and Raikou. Like the legendary birds before them, these Pokemon are related very closely with each other. It is said that they were all trapped in the brass tower in the Johto region, resulting in their deaths, until Ho-Oh resurrected the three beasts and allowed them to once again roam the land. Although their types and domains are identical to that of the legendary birds, these beasts govern the Johto region and are land based rather than sky based. The legendary beasts have appeared in numerous games, and Entei and Suicune both had their own movies as well.
Tower Duo (Ho-oh and Lugia)
Ho-Oh and Lugia are considered to be polar opposites of each other. Long ago, they resided on two tall standing towers in Ecruteak city, but lightning struck and destroyed the Brass Tower (Lugia's home), and they both fled the area. Although Ho-Oh plays a more important role in the generation 2 Pokemon games, having brought about the creation of the Legendary Beasts, Lugia has a movie dedicated to him, in which he is linked with the Legendary Birds of the first generation. In the movie, Lugia is responsible for quelling the conflict between the three birds.
Celebi (Mythical Pokemon)
Celebi is a mythical Pokemon like Mew. In terms of power and scope, they are comparable to legendary Pokemon, but are far rarer. Celebi is considered the guardian of the forest (specifically Ilex forest in the Johto region, and is able to travel through time in order to protect it. Celebi is the star of Pokémon's fourth movie, Celebi: The Voice of the Forest, and is considered very similar to Mew in terms of size, statistics, and status in the Pokemon world. These traits are actually shared among many mythical Pokemon.
Generation 3
Regigigas and the Legendary Titans (Regirock, Regice, and Registeel)
Technically, Regigigas was introduced in Generation 4, but it is placed here on the list because of his relation to the other titans. Generation 3 began the trend of explaining legendary Pokémon's legendary status by placing them in the mythos of the Pokemon world itself. Regigigas, an ancient titan pokemon, is said to have moved the continents into place, aiding in the formation of the world in ancient times. Additionally, Regigigas is known as the master of the legendary titans, as he actually is the one who created them. Regirock, Regice, and Registeel all were formed from clay, ice, and magma respectively by Regigigas in ancient times. Little is known about these enigmatic pokemon, except that people of ancient times saw Regigigas as too powerful to be left alone and decided to seal him away in Snowpoint Temple.
Eon Duo (Latias and Latios)
Latias and Latios are unique in that they are not connected to any great myth or purpose, but rather are simply extremely rare and powerful pokemon. The two look nearly identical, distinguishable only by their size and color, and have made appearances in many forms of Pokemon media, even having a movie dedicated to the pair. In this movie, the two Pokemon are responsible for guarding the city of Alto Mare, but this was never replicated in any game.
Weather Trio (Groudon, Kyogre, and Rayquaza)
The stars of Pokémon's third generation games, Ruby, Sapphire, and Emerald, are Groudon, Kyogre, and Rayquaza. Once again, these Pokemon play a huge role in the creation of the world of Pokemon, with Groudon being responsible for all land, Kyogre for all water, and Rayquaza for all the skies. The villainous teams Aqua and Magma from Pokemon Ruby and Sapphire seek to awaken these legendary Pokemon and utilize them to completely fill the world with water or land respectively. The world was essentially created by the constant battling between Groudon and Kyogre and prevented from being destroyed by the interference of the peace-keeping Rayquaza.
Jirachi and Deoxys (Mythical Pokemon)
Jirachi and Deoxys are yet more mythical Pokemon. Jirachi, like Mew and Celebi before, is diminutive in size and also is a psychic type Pokemon with a penchant for immense power. Although Jirachi does not play a huge role in the games, the sixth Pokemon movie, Jirachi: Wish Maker, focuses entirely on this Pokemon. It is believed that Jirachi only wakes up for seven days every thousand years and is able to grant wishes during this time. By contrast, Deoxys breaks the mold of the mythical Pokemon seen until now. Deoxys is a Pokemon from space and is very strange even by Pokemon's standards, with the ability to morph into different forms at will. Deoxys also did not play a huge role in most games, but is the star of the seventh Pokemon movie, Destiny Deoxys.
Generation 4
Lake Guardians (Mesprit, Uxie, and Azelf)
The lake guardian legendary trio, so named because they guard Lake Acuity, Lake Verity, and Lake Valor of the Sinnoh region, were created by Arceus, the Original One. These beings represent consciousness, with Mesprit influencing emotion, Uxie influencing knowledge, and Azelf influencing willpower. These Pokemon have the unique ability of calming and, to a certain extent, controlling the creation trio, and in Pokemon Diamond and Pokemon Pearl aid the player in doing so. They also have made appearances in the anime and its many movies, though they are not given as much attention as other legendaries.
The Lunar Duo (Cresselia and Darkrai)
Cresselia and Darkrai, dubbed the lunar duo, represent a crescent moon and new moon respectively. Cresselia is associated with hope and good dreams and plays a very minor role throughout games and the anime, while Darkrai is associated with dread and nightmares. Although the main entries indicate that Darkrai harbors no ill intentions towards other Pokemon or humans, he has been used as a villain in movies and offshoot games, namely the Pokemon Mystery Dungeon series in which he is seen as the counterpart to Cresselia. It is also worth noting that while Cresselia is considered a legendary Pokemon, Darkrai is instead classified as a mythical Pokemon.
Heatran and Shaymin
Though Heatran is a minor legendary Pokemon, it is certainly an ancient one. Heatran is said to represent the core of the planet and was born when the creation trio created Sinnoh. Heatran does not play a major role, but it is notable as the only legendary Pokemon with gender. Shaymin, on the other hand, is a mythical Pokemon, capable of restoring life to dying land and posessing two forms, a Land Form and a Sky Forme. Like Heatran, this Pokemon is mostly irrelevant in terms of lore and inclusion in the story of certain games or the anime.
Creation Trio (Dialga, Palkia, and Giratina)
Taking the influence of legendary Pokemon to cosmic heights, generation 4's creation trio, consisting of Dialga, Palkia, and Giratina, are attributed with the creation of world. Dialga exhibits mastery over time, and created time itself, while Palkia has mastery over space and is credited for its creation. Giratina, on the other hand, resides in the Distortion World and governs anti-matter. These creatures aren't concerned with good and evil, but Giratina does step in to prevent the world's destruction at the hands of Cyrus towards the end of Pokemon Platinum. All three Pokemon, like the lake guardians trio, were created by Arceus and tasked with the creation of the universe.
Manaphy and Phione (Mythical Pokemon)
Manaphy and Phione are unique in many ways. For starters, their status as mythical Pokemon is entirely up for debate, as numerous official sources contradict each other in this regard. That said, Manaphy's stature and stat spread point towards it being a mythical Pokemon like Mew, Celebi, and Jirachi, although it would be the first to lack the psychic type. Additionally, Phione can only be obtained by breeding Manaphy with a ditto, making Manaphy the only mythical Pokemon capable of breeding as well. These Pokemon possess the special power to bond with any Pokemon they come in contact with.
Arceus
The final entry here is easily the most powerful and impressive of them all. Arceus, also known as the Original One, is responsible for the creation of the Sinnoh region and likely the entire Pokemon Universe. Arceus created Dialga, Palkia, and Giratina to master time, space, and anti-matter, then created the lake guardians as a way of taming the dragons. It is said that this Pokemon hatched from an egg before the universe existed and then built everything that exists. This Pokemon fits the rules for mythical Pokemon but receives a lot more attention from characters in the games.
Legendary and mythical Pokemon play a huge role in the mythos of the Pokemon world, often contributing to the creation myth or having some important task which they spend their endless lives fulfilling. These powerful Pokemon have fascinated fans for years, and with each generation, the pantheon seems to grow to new heights. Although some legendary Pokemon seem lackluster compared to others, it is possible that these Pokemon simply haven't gotten their spotlight yet. Regardless, even if certain groups like the legendary birds and beasts don't quite hold up to the epic proportions put in play by the likes of Arceus and the creation trio, it cannot be denied that they are certainly mystical and powerful Pokemon altogether.