A little note
So, someone asked me about a Pokémon I have quite a bit of theories on, but no concrete evidence. Don't worry, I will get to it, it's just going to be a long while. Especially since I have a little trip planned to go visit a certain tree in a certain place known to have a certain little kitty in the spring.
Most of my theories about Mew actually come from observations and knowledge on Mewtwo, who I have an abundance of information on because well. Meyu. Meyu has attempted to get those confirmed or denied by the other legendaries and mythicals, but everyone's got their mouths shut on the subject. Ditto has also been a small part, I even made a post explaining my theory on how they're connected.
That being said, I'm still going to list those theories in a bullet point format,
Mew lived in groups. Meyu is a very social Mewtwo, as a matter of fact he's actually even known as "the social clone" among the legendaries. However, the other two clones of Mew are still somewhat social, despite how dulled down it was, as both of the other clones prioritized power over, you know, not lashing out violently against those who have wronged it. Meyu was made to better study Mew, as well as to gain knowledge on Mewtwo's biology. They were willing to risk sacrificing the raw power the clone is known for for a more compassionate temperament.
Mew are omnivorous, with a marked preference for sweeter berries or meat, though they hunted alone.
Mew reproduced sexually. I'm not explaining that.
Mew raised their kits together, a theory based on how Meyu tends to handle children in general, but especially baby pokemon and babies, something I observed with one of my cousin's newborn last time I was in Alola
Mew helped young gain control over their psychic abilities through exposure. Same reasoning as above.
I have more but It'd take a lot longer to list all of them.