It is not known to evolve into or from any other Pokémon.
It is often considered to be part of the Tower duo with Ho-Oh, even sometimes as Ho-Oh's polar opposite. Silver represents Lugia as "guardian of the seas", and Gold represents Ho-Oh as "guardian of the skies." Lugia is also the trio master of the Legendary birds.
Lugia is a large Pokémon that resembles a dragon, a plesiosaur, and a bird. It is primarily pale silver-white, but it has blue undersides with slightly varying tones. It has a ridged mouth similar to a beak, although it has pointed teeth on its lower jaw. Its head has a point to the back, and Lugia's eyes have pointed blue or black spikes on them. Lugia has a long, slender neck and a smooth, streamlined body. Dark blue or black plate-like protrusions run down the length of its back, and there are two smaller, more pointed ones on the end of its tail. It can fold back these plates to increase its speed. It has large wings that resemble hands. Though it is genderless, a young Lugia has been observed, suggesting that there is a breeding population. Lugia has been shown to be fiercely protective of its young.
Lugia leads the legendary birds. When they fight over territory, Lugia is the only Pokémon that can quell their ceaseless fighting, as observed in the second Pokémon movie. Much like the birds, it possesses the ability to control the weather; most notably, it can calm and give rise to storms. It is said that a light flutter of its wings is capable of causing winds powerful enough to tear down cliffs. If it were to flap its wings, it could hypothetically spawn storms lasting as long as 40 days. It is highly intelligent, and because of the devastating power it could accidentally inflict, it isolates itself deep underwater and tends to sleep in solitude. Lugia is the only known Pokémon that learns Aeroblast. It is extremely rare and is hardly ever seen.
The Masked Man apparently caught Lugia twice (its plucked feather item Silver Wing is shown under his possession several years ago, only to be stolen by Green), but both times it went back to the wild along with Ho-Oh.
When released from a Poké Ball, Lugia will fly up out of the stage and return in the background, where it unleashes a powerful Aeroblast on a section of the stage.
Melee trophy information
The waters of the Whirl Islands are home to this legendary Pokémon, whom very few have seen. Lugia live quietly in the deepest ocean trenches for one very good reason: its combined aerial and psychic powers are so strong as to be extremely dangerous. The special moves of this gargantuan creature include the destructive wind assault known as Aeroblast.
Brawl trophy information
"A Diving Pokémon. A legendary Pokémon often referred to as 'guardian of the seas,' it has the impressive ability to control the wind. Lugia typically spends its time quietly at the bottom of the ocean. Highly powerful in all areas, Lugia's Aeroblast move is especially powerful. It uses strong flapping of its wings to target damage on a foe's weak spot."
3DS/Wii U trophy information
NA: Despite being a Psychic/Flying-type Pokémon, Lugia sleeps on the ocean floor. Legend says the flapping of Lugia's wings can create storms that last up to 40 days. It's impossible to know for sure, but in Smash Bros., Lugia definitely brings a storm with its Aeroblast attack.
PAL: Despite being a Psychic- and Flying-type, Lugia sleeps on the ocean floor. It's said that if it were to flap its wings on waking up, it could cause a storm lasting 40 days. No one can say whether that's true or not, but Lugia's attacks certainly make it seem so. It flies behind the stage and creates a mighty gust of wind with its Aeroblast attack.
This Pokémon was unavailable prior to Generation II.
Lugia's aquatic tendencies could relate it to plesiosaurs. It is also possible that Lugia may be based on Ryūjin, a dragon who lived on the ocean floor and was the Shinto god of the sea. The two have similarities in mythology, and Lugia's Shiny colors (red and white) are the same colors as the coral Ryujin's palace was made of. In addition, it is worth noting that dragon (yang, male, water) and phoenix (yin, female, fire) duality is prevalent in Eastern mythology, and Ho-Oh clearly resembles a phoenix. Lugia may also be an embodiment of storms. Lugia's avian body, coloration, and face-markings suggests that it may be somewhat based on the grey heron. The beluga whale, a white whale with a similar body shape and coloration to Lugia, may also be a basis for Lugia's design and name. Lugia's back fins and tail spikes are reminiscent of the Stegosaurus.
Lugia may be derived from lutetium (a silverish element), which in turn is named after Lutetia (the Roman name for Paris, the city of light). It may also involve Lugeo (Latin for to lie dormant, alluding to the way Lugia lies at the bottom of the sea) and luna (Latin for moon). Alternatively, it may come from beluga whale. It may also incorporate deluge.
In other languages
From lutetium, Lutetia, lugeo, luna, and beluga whale