Is it legit?

[PokeTony]

Hello everyone, I have been Pokemon for a long time, I think since blue, but then just recently came back for Omega Ruby.

So i'm new to this whole shiny pokemon & hunting, and most importantly the legendaries. 

So yesterday a friend that I know has been playing Pokemon since birth, lol and I really wanted Jirachi and he actually gave me one...

So it looks legit and everything, but I was reading that legendaries are SUPPPPPER hard to come by so I was just wondering
is it legit? How can I tell?

He also showed  me a Shiny Mew he had and he said he was willing to trade it to me if I really wanted it but I said no....
is this legit / real or is he hacking them?

Also another question: Let's say he gives me that shiny Mew and it's hacked and I want to use it online and stuff, will I get banned or something?

I just want legit Pokemon...I was alarmed when he  gave me Jirachi and willing to give me a Shiny Mew.

I was reading that Shiny Mew is literally almost impossible or something called "shiny lock"

Thank you.