From Bulbapedia, the community-driven Pokémon encyclopedia.
A legendary duo is a pair of closely related Pokémon, either representing teamwork or opposition. Much like how every main region has at least one legendary trio, every main region, besides Unova, also has a legendary duo. In the games, they are often found after the player gets past the Elite Four but often aren't as important in the main storyline as the trios are. Duos are featured in several of the movies, either in their respective pairs, or on their own, as a keeper of peace. Sometimes pairs of Pokémon once thought to be legendary duos are revealed to actually be legendary trios upon the release of the third version, and even within trios, the dynamic between two members is very close to that of a duo. Kyogre and Groudon, Dialga and Palkia, Tornadus and Thundurus or Reshiram and Zekrom are prime examples of that.
These duos are pairs of Pokémon with similar stats, movesets, and related with lore; the members are usually presented as equals, and function in a symmetrical dynamic.
The Tower Duo
Lugia and Ho-Oh in promotional art for the TCG
The tower duo is the legendary duo of Johto that consists of Lugia and Ho-Oh. Lugia and Ho-Oh are often regarded as polar opposites. Lugia represents the moon, sea, storms, the color silver and is the mascot of Pokémon Silver and Pokémon SoulSilver, while Ho-Oh represents the sun, sky, rainbows, the color gold, and is the mascot of Pokémon Gold and Pokémon HeartGold. Both are also trio masters; Lugia is the master of the legendary birds, while Ho-Oh is the master of the legendary beasts.
Their legend is introduced in Generation II, and states that the two birds each resided on a tower: Lugia on the Brass Tower, and Ho-Oh on the Bell Tower. When the Brass Tower was destroyed in Johto (prior to the start of the second generation games), the pair was split up thus creating the legendary beasts: Entei, Raikou, and Suicune.
The Eon Duo
- Main article: Eon duo
Latias and Latios artwork
The eon duo is a legendary duo of Hoenn that consists of Latias and Latios, which are also that region's roaming Pokémon. The two share their typing, two of their base stats and even several moves they learn when they level up. Both were featured in the movie Pokémon Heroes, where they were revealed to be playful siblings.
Latios and Latias take on counterpart availability in Pokémon Ruby, Sapphire, and Emerald as well as Pokémon HeartGold and SoulSilver, with Latios being a roaming Pokémon in Ruby and SoulSilver, and Latias doing the same in Sapphire and HeartGold. In Emerald, after the player has defeated the Elite Four, their mother will ask if the Pokémon mentioned on TV was red or blue, and depending on that, one of the two will be roaming Hoenn. The other member of the duo will be found on Southern Island, accessible by Eon Ticket, in Ruby, Sapphire, and Emerald, and in Pewter City, through the Enigma Stone event, in HeartGold and SoulSilver.
The Lunar Duo
The lunar duo is a legendary duo of Sinnoh that consists of Cresselia and Darkrai. Cresselia and Darkrai are commonly seen as polar opposites, just like the aforementioned Johto bird duo of Lugia and Ho-Oh. Also, Cresselia and Darkrai reside on Fullmoon Island and Newmoon Island respectively, which are direct mirror images of each other. Cresselia and Darkrai are also known as the subconscious duo because of how Darkrai is said to give people nightmares, while Cresselia does the opposite (giving people pleasant dreams). Furthermore, Cresselia and Darkrai also appear in Pokémon Mystery Dungeon: Explorers of Time, Explorers of Darkness and Explorers of Sky as enemies.
They made their anime debuts in Sleepless in Pre-Battle! where they battled one another.
Those duos are made up of Pokémon with a strong relation in the lore, but their stats and movesets tend to be fairly distinct and not equivalent; these duos can be said to be asymmetrical compared to the true duos.
The Mew Duo
Mewtwo and Mew make up Kanto’s legendary duo. They are both very elusive, if not unique, Psychic-type Pokémon. Mewtwo was cloned from Mew, meaning the two share DNA and many traits. In the games, however, they are usually treated as unrelated Pokémon, with Mewtwo's stats, moveset and treatment in the Pokémon Stadium series being closer to that of the Tower Duo, while Mew's are closer to that of Celebi.
In Mewtwo Strikes Back, Mew embodied innocence and joy, but Mewtwo's experiences as it gained consciousness gave it a jaded and cynical view of humanity. The duality expressed between the two characters formed the basis of their conflict, but innocent Mew, with the help of Ash Ketchum, is able to sway Mewtwo's contempt.
The Sea Guardian Duo
Manaphy is the only legendary Pokémon so far that is able to breed. The outcome however is a separate species, Phione. In a way the sea-fairy duo are a perfect counterpart to the Mew-duo; instead of an unnatural (through genetic engineering in lab), stronger version, Phione is a natural (through breeding), weaker version of Manaphy; both also appear before the "original" in the Pokédex. Due to conflicting evidence from official sources, Phione's status as a legendary Pokémon is uncertain; if it is not a legendary Pokémon, the sea guardian duo is not a legendary duo.
- Both the tower duo and the eon duo were seen in the anime before their respective generations. Ho-Oh was seen in Pokémon - I Choose You! and Lugia was seen in The Power of One. Both Latias and Latios were seen in Pokémon Heroes, the fifth movie.
- Ho-Oh and Lugia are the only trio masters that are part of a legendary duo.
- The lunar duo is the only duo that has Pokémon which aren't next to each other in the Pokédex.
- Furthermore, the lunar duo is the only duo that doesn't have any Pokémon in a regional Pokédex.
- The lunar duo are also the only duo not to share at least one type.
- Despite Mewtwo being an altered clone of Mew, thus closer related than any other duo, statistically they are very different; with different stat totals, unrelated stat distribution, and divergent level up movesets; in those fields, Mewtwo seems closer to Lugia and Ho-Oh, while Mew seems more similar to Celebi, especially in Generations II and III.