Here's a list of all Legendary Pokémon in the National Pokédex, including some that are considered Mythical Pokémon:
Generation 1:
* Articuno (Ice/Flying)
* Zapdos (Electric/Flying)
* Moltres (Fire/Flying)
* Mewtwo (Psychic)
* Mew (Psychic)
Generation 2:
* Raikou (Electric)
* Entei (Fire)
* Suicune (Water)
* Lugia (Psychic/Flying)
* Ho-Oh (Fire/Flying)
* Celebi (Psychic/Grass)
Generation 3:
* Regirock (Rock)
* Regice (Ice)
* Registeel (Steel)
* Latias (Dragon/Psychic)
* Latios (Dragon/Psychic)
* Kyogre (Water)
* Groudon (Ground)
* Rayquaza (Dragon/Flying)
* Jirachi (Steel/Psychic)
* Deoxys (Psychic)
Generation 4:
* Uxie (Psychic)
* Mesprit (Psychic)
* Azelf (Psychic)
* Dialga (Steel/Dragon)
* Palkia (Water/Dragon)
* Giratina (Ghost/Dragon)
* Cresselia (Psychic)
* Phione (Water)
* Manaphy (Water)
* Darkrai (Dark)
* Shaymin (Grass)
* Arceus (Normal)
Generation 5:
* Victini (Psychic/Fire)
* Cobalion (Steel/Fighting)
* Terrakion (Rock/Fighting)
* Virizion (Grass/Fighting)
* Tornadus (Flying)
* Thundurus (Electric/Flying)
* Landorus (Ground/Flying)
* Reshiram (Dragon/Fire)
* Zekrom (Dragon/Electric)
* Kyurem (Dragon/Ice)
* Keldeo (Water/Fighting)
* Meloetta (Normal/Psychic)
* Genesect (Bug/Steel)
Generation 6:
* Xerneas (Fairy)
* Yveltal (Dark/Flying)
* Zygarde (Dragon/Ground)
* Diancie (Rock/Fairy)
* Hoopa (Psychic/Ghost)
* Volcanion (Fire/Water)
Generation 7:
* Tapu Koko (Electric/Fairy)
* Tapu Lele (Psychic/Fairy)
* Tapu Bulu (Grass/Fairy)
* Tapu Fini (Water/Fairy)
* Cosmog (Psychic)
* Cosmoem (Psychic)
* Solgaleo (Psychic/Steel)
* Lunala (Psychic/Ghost)
* Necrozma (Psychic/Dragon)
* Magearna (Steel/Fairy)
* Marshadow (Fighting/Ghost)
* Poipole (Poison)
* Naganadel (Dragon/Poison)
* Guzzlord (Dark/Dragon)
* Type: Null (Normal)
* Silvally (Normal/??? (Type changes based on Memory))
Generation 8:
* Zacian (Fairy/Steel)
* Zamazenta (Fighting/Steel)
* Eternatus (Dragon/Poison)
* Kubfu (Fighting)
* Urshifu (Water/Fighting)
* Calyrex (Psychic/Grass)
* Glastrier (Ice)
* Spectrier (Ghost)
Generation 9:
* Koraidon (Dragon/Electric)
* Miraidon (Dragon/Electric)
* Ogerpon (Normal/??? (Type changes based on form))
* Tausk (Fairy)
* Tinkaton (Fairy/Steel)
* Chi-Yu (Fire/Psychic)
* Ting-Lu (Rock/Ground)
* Chien-Pao (Dark/Fighting)
* Wo-Chien (Ghost/Grass)
* Iron Valiant (Steel/Fighting)
* Great Tusk (Dragon/Ice)
* Iron Bundle (Dragon/Steel)
* Dondozo (Water)
* Tatsugiri (Water/??? (Type changes based on form))
Mythical Pokémon:
* Manaphy (Water)
* Darkrai (Dark)
* Shaymin (Grass)
* Victini (Psychic/Fire)
* Keldeo (Water/Fighting)
* Meloetta (Normal/Psychic)
* Genesect (Bug/Steel)
* Diancie (Rock/Fairy)
* Hoopa (Psychic/Ghost)
* Volcanion (Fire/Water)
* Jirachi (Steel/Psychic)
* Phione (Water)
* Celebi (Psychic/Grass)
* Mew (Psychic)
* Cresselia (Psychic)
* Marshadow (Fighting/Ghost)
* Poipole (Poison)
* Magearna (Steel/Fairy)
* Zarude (Dark/Grass)
* Meltan (Steel)
* Melmetal (Steel)
* Calyrex (Psychic/Grass)
* Glastrier (Ice)
* Spectrier (Ghost)
* Tausk (Fairy)
This list is complete as of the release of Pokémon Scarlet and Violet.
It's important to note that some Pokémon, like Silvally and Ogerpon, have multiple forms that change their types. The type of a Pokémon can also be affected by held items, abilities, and other factors.