WikipedaMew appears as a pink feline-esque Pokémon with short arms, long feet, large blue eyes, and a long tail. Its skin is covered with a layer of fine pink hair. In the 3D games, it is shown to be white with pink bits on its feet, tail, and head. It seems to be genderless as well. The Cinnabar Mansion Journals (4 diaries found in Cinnabar Mansion) state that Mew 'gave birth' to Mewtwo, Mewtwo was genetically altered by the author (probably with the aid of his fellow researchers) of the Cinnabar Mansion Journals diary. This is explained in both the plot of Pokémon: The First Movie and Mewtwo's Pokedex entry.
By nature, Mew is known to be a playful, but wise, Pokémon that acts benevolently towards all other Pokémon. Its DNA is said to possess the genetic composition of all existing Pokémon species. If it's DNA does contain all the genetic compositions of every other Pokémon, it is safe to say that Mew may have been the first Pokémon and they evolved over time to today's modern species. It is capable to use seemingly all known Pokémon techniques. In addition to its wildly variable techniques, Mew can also transform into another Pokémon in the same manner as Ditto. It is also capable of instant teleportation, summoning giant pink bubbles of psychic energy, and making itself invisible at will.
It should be noted that Mew also bears a resemblance to a fetus. Its tail is somewhat reminiscent of an umbilical cord, it is most often seen in a pose similar to that of the fetal position, and it flies in a bubble that is analogous to an amniotic sac. This "embryonic" form can be thought of as a precursor to all forms of Pokémon, much like how many animals' embryos appear similar in the early stages of development. This lends further support to the hypothesis that Mew is, in fact, the ancestor of all Pokémon, or at least a being with the potential to develop into any form of Pokémon, much like a human stem cell; this may also explain why Mew can transform into other Pokémon and use all other Pokémon techniques. If Mew is indeed the ancestor of all Pokémon, that would make it (or its species)older than Kyogre, Groudon, and even the legendary Rayquaza. According to a recent poll on the official Pokémon website, Mew is currently the most popular Legendary Pokémon.