Mew is an unsolved mystery. Its DNA is said to contain the genetic code of all Pokémon, so it is believed to be the oldest ancestor of Pokémon in existence.
Despite this, this mischievous Pokémon is young at heart, appearing to those it senses are purely good with naught a reason but to play with them. It is incredibly intelligent and far more powerful than it looks, but at the end of the day, it just wants someone to play with.
I warned you about that cuteness factor, didn’t I?