The Pokémon anime occasionally diverges from the games, sometimes in minor ways like evolving mid-battle, and sometimes in major ones. One of the biggest divergences occurred when the Pokémon anime introduced something never seen before: a baby Legendary Pokémon.
Legendary Pokémon in the games are generally unable to breed, which helps to maintain their Legendary Pokémon rarity. Many don't even have an identifiable gender, and even those that do can't breed. The one Mythical Pokémon who can breed, Manaphy, actually creates a whole new species, Phione, rather than more Manaphy. That means that while many Pokémon have distinct baby forms, like Pichu is to Pikachu, Legendaries have rarely been shown as anything other than full-size adults. While Mewtwo had a younger form in the first Pokémon movie, the creature's unnatural creation sets it apart from another young legendary shown by the anime.
In a three episode arc that begins with "The Mystery is History," Ash and friends, including recurring character Richie, meet a young boy named Oliver who is playing with a mysterious creature under the surface of the water. The creature turns out to be Lugia--but not the Lugia from the second movie (although Ash does mention it). Instead, this is a "baby" Lugia named Silver, which looks identical to a normal Lugia aside from being very small. Unfortunately, Team Rocket's Butch and Cassidy have also set eyes on the Lugia, and report it to a superior, who refers to it as "Mysterious Pokémon X." They eventually steal it successfully, and the angry parent Lugia arrives to teach Team Rocket a lesson, only to get captured as well. Ash and friends must then release the two Lugia, defeat Team Rocket, and save the day.
Baby Lugia Has Huge Implications for Legendary Pokémon
This baby Lugia raises a lot of questions about how Legendary Pokémon grow and mature. Some Legendaries, like Cosmog, are capable of evolution, but most aren't, and Cosmog is a bit of a special case anyway. While Pokémon evolution doesn't directly correlate with maturity, the two are often closely linked in the anime, so the only way to convey that a Lugia was young was to make it much smaller. This does suggest that Legendary Pokémon might actually grow and mature more like real animals do, and they might even give live birth rather than hatching eggs--something suggested by the Red and Blue journal entries about Mew. That might offer an explanation as to why Legendary Pokémon are incapable of laying eggs, as that's not how they reproduce.
Interestingly, the Lugia in the episode is only ever referred to as "the parent" Lugia, and there is only one parent, so perhaps some form of asexual reproduction could be at work among Legendaries instead. Baby Legendaries are also seen again in the movie Pokémon Heroes: Latios and Latias, where baby Latios and Latias Pokémon are shown at the end of the film alongside the ones mentioned in the title. They are similarly depicted as small versions that are otherwise identical to their fully grown state, confirming that this is just how Legendary Pokémon work, at least in the anime.
The biology behind Legendary Pokémon may never be properly explained to diehard fans, but episodes like this give a tantalizing glimpse into an area of the Pokémon world that's rarely addressed.
