seriously, people on youtube only say by hack or just troll so can you tell me please?
The only way to get a legit Mew in X/Y or ORAS is to trade, unless there is an even. (there have been Mew events in previous games.)
In the american version (maybe in the Japan version too) of Pokemon Red and Blue (or was it Red an Green) there is a glitch that allows you to catch Mew, not technically legit, but still legit.
Starting February 1, 2016 and endin on Feb. 24, you can get a code for Mew. You then have to go to GameStop and get the code, then go to Mystery Gift, Get With Code, then talk to the Delivery Girl in a Pokemon Center and get Mew. It'll be Level 100 and know Pound. The same goes for Darkrai (May 1-24), Arceus,(Aug. 1-24) and Genesect (Nov. 1-24).
Hope This Helps!!!
Events are by far the easiest way to get a Mew. There are also glitches you can use on the Gen 1 games to obtain a Mew although you can only transfer using the versions bought on the 3DS and I'm not sure if the glitch still exists in these versions. The only set in stone way you can still obtain a Mew is to purchase a third string game for the Wii called "My Pokemon Ranch". It was a game you could transfer Pokemon to from your Gen 4 game. If you transfer 999 Pokemon to the Ranch, the NPC in the game will offer to trade a Mew to you for another Pokemon that will be specified. I believe you can also get a Phione using this method but with 500 Pokemon instead. You can transfer this Mew to your Gen 4 game and then use the transfer methods necessary to get your Mew up to the newest generation. Hope this helps.