Are there legendary Pokémon in the mainline games?

 Yes, legendary Pokémon are a recurring element in the mainline Pokémon games. Legendary Pokémon are rare and powerful creatures that often play a significant role in the game's story, lore, and gameplay. These Pokémon are usually one-of-a-kind or very limited in number within the Pokémon world.

Legendary Pokémon are known for their unique designs, abilities, and sometimes their connection to in-game events or specific locations. Some legendary Pokémon include well-known figures like Mewtwo, Lugia, Ho-Oh, Rayquaza, Dialga, Palkia, Giratina, Kyogre, Groudon, and many more.

In addition to regular legendary Pokémon, there are also Mythical Pokémon, which are even rarer and often distributed through special in-game events or promotions. Some Mythical Pokémon include Mew, Celebi, Jirachi, and more.

These legendary and mythical Pokémon are often sought after by trainers for their power and unique attributes, and they are a key part of the Pokémon lore and gameplay in the mainline games. Players typically encounter them during the main storyline, through in-game events, or in special locations where they are central to the game's plot or post-game content.

Mewtwo: Known for its psychic abilities, Mewtwo is a clone of the mythical Pokémon Mew. It has appeared in multiple Pokémon games and is often associated with the pursuit of scientific experimentation.

Lugia and Ho-Oh: Lugia and Ho-Oh are associated with the Johto region. They represent the sea and the sky, respectively, and have central roles in the storyline of Pokémon Gold and Silver.

Rayquaza: A powerful Dragon/Flying-type Pokémon, Rayquaza is known for its central role in the storyline of Pokémon Ruby and Sapphire, where it resolves the conflict between Kyogre and Groudon.

Dialga, Palkia, and Giratina: These legendary Pokémon are known as the "Creation Trio" and are central to the Sinnoh region's lore. Dialga controls time, Palkia controls space, and Giratina represents antimatter.

Kyogre and Groudon: These legendary Pokémon represent the forces of the sea and land, respectively, and are central to the storyline of Pokémon Ruby and Sapphire.

Arceus: As previously discussed, Arceus is often considered the "God of Pokémon" and is associated with the creation of the Pokémon world.

Mew: Mew is a mythical Pokémon known for its genetic versatility and is said to contain the DNA of all other Pokémon species.

Celebi: A time-traveling Pokémon, Celebi is often associated with time-related events and is considered a guardian of the forest in the Johto region.

Jirachi: Jirachi is known for granting wishes when it awakens once every thousand years.

Darkrai and Cresselia: These Pokémon are often associated with dreams and nightmares and have featured in various in-game events and storylines.

Regirock, Regice, and Registeel: These golem-like Pokémon are known as the "Legendary Titans" and were introduced in the Hoenn region. They are often found in special caves and are associated with puzzles to unlock their locations.

Heatran: Heatran is a Fire/Steel-type Pokémon that dwells in volcanic caves. It plays a role in the Sinnoh region's lore and is known for its association with intense heat.

Cobalion, Terrakion, and Virizion: These Pokémon, collectively known as the "Swords of Justice," are part of a group of legendary Pokémon introduced in the Unova region. They are associated with themes of justice and heroism.

Zygarde: Zygarde is a Dragon/Ground-type Pokémon introduced in the Kalos region. It is known for its unique ability to change forms, including a 10% Forme and a Complete Forme.

Solgaleo and Lunala: Solgaleo and Lunala are Legendary Pokémon introduced in the Alola region. They are associated with the sun and moon, respectively, and play central roles in the storyline of Pokémon Sun and Moon.

Magearna: Magearna is a Mythical Pokémon known for its mechanical appearance and is associated with advanced technology. It was introduced in the Alola region.

Necrozma: Necrozma is a Psychic-type Pokémon known for its ability to absorb light. It is featured in the Alola region's storylines and plays a central role in the Pokémon Ultra Sun and Ultra Moon games.

Zeraora: Zeraora is an Electric-type Mythical Pokémon introduced in the Alola region. It is known for its impressive speed and electrical powers.

Zacian and Zamazenta: These Pokémon are Legendary Pokémon introduced in the Galar region. They are associated with the Sword and Shield, respectively, and play important roles in the storyline of Pokémon Sword and Shield.

Eternatus: Eternatus is a Legendary Pokémon introduced in the Galar region, known for its connection to the energy crisis in the storyline of Pokémon Sword and Shield.

Giratina: Giratina is a Ghost/Dragon-type Legendary Pokémon known for its connection to the Distortion World, a parallel dimension. It was introduced in the Sinnoh region.

Phione: Phione is a Mythical Pokémon known for its ability to breed, producing more Phione. It is related to the Legendary Pokémon Manaphy.

Manaphy: Manaphy is a Mythical Pokémon with the unique ability to breed Phione when held in the Day Care Nursery. It was introduced in the Sinnoh region.

Shaymin: Shaymin is a Mythical Pokémon with two forms, Land Forme and Sky Forme. It is associated with flowers and was introduced in the Sinnoh region.

Regigigas: Regigigas is a Normal-type Legendary Pokémon known as the "Colossal Pokémon." It is said to have created the Regi trio (Regirock, Regice, Registeel) and was introduced in the Sinnoh region.

Landorus, Thundurus, and Tornadus: These Legendary Pokémon are known as the "Forces of Nature" and were introduced in the Unova region. Each represents a different aspect of nature and weather.

Meloetta: Meloetta is a Mythical Pokémon with two forms, Aria Forme and Pirouette Forme. It has a musical theme and was introduced in the Unova region.

Xerneas and Yveltal: These Legendary Pokémon were introduced in the Kalos region. Xerneas is associated with life and Yveltal with destruction.

Diancie: Diancie is a Mythical Pokémon associated with diamonds and was introduced in the Kalos region.

Volcanion: Volcanion is a Mythical Pokémon with Fire/Water typing and was introduced in the Kalos region.