I am not positively sure about mew cuaz there are so much hacks that go around with this pokemon I personally don't rng 3rd gen but I know for sure and was told that pokecheck isn't best to look at as well cuaz it kinda stinks at checking 3rd gen mons but the only mew i know that is legal is the eppie mew that is shiny. I just have a feeling it is a hack but dewey may be more help then i am silver do to my lack of the 3rd gen rnging cuaz i had a mew before shiny and it was hacked and looked clean on check.Ahhh, I see. So in this case, while I know it's possible to obtain this one, I'm unsure if getting this IV spread is possible.
I got this particular Mew in a trade recently (it was likely cloned), and it seems to check out. Though I'd like to get a second opinion on it.
Pokemon Species: Mew
Nickname: ミュウ (Mew in Japanese)
OT Gender: Cannot be determined.
EV's: 6 HP / 252 SpAtk / 252 Speed
IV's: 31/31/31/31/31/31 (Flawless, according to IV judge.)
Characteristic: Takes plenty of siestas.
Moves: Nasty Plot, Psyshock, Aura Sphere, Dark Pulse
Level Caught at: Doesn't say.
Current Level: 100
Location Caught: A fateful encounter seems to have led it across space and time to reach the Kalos region from the Hoenn Region.
Pokeball Caught In: Poké Ball
Any other notes?: None.
not sure if you know but 3rd gen checking on pokecheck isn't that good just letting you know so the mew can still come up clean and can be hacked.