The Mew glitch (I'm assuming you're talking about the one that involved the Gambler on rt.7 and the youngster on rt.25, right?) doesn't work in FRLG for obvious reasons.
The only legitimate way of getting Mew is through Nintendo events. >_>
Pretty much that. I think after 10 years, Nintendo would have caught on to the infamous Mew glitch, so there's no reason it should be in FRLG. Next time, please use the simple questions and answers thread.