Ok so if you really want to transfer a Pokemon all the way from Pokemon Ranch to ORAS, here's what you need to do:
First of all, you need Pokemon Diamond or Pearl. Next you need Black, Black 2, White, or White 2. You'll need 2 DS systems (this can be 3DS and 3DS, DS and DS, DSI, whatever. you can use any system that has DS in the title). You also need the 3DS app Pokemon Bank (as well as the app that goes with it, Poke Transporter), and a subscription to it (five dollars per year).
First, transport the Pokemon to Diamond/Pearl (you can't transfer it to Platinum)
To do this, you need to trade an egg in Pokemon Diamond or Pearl for the Mew.
Follow the steps in this video
After you have the Pokemon in your D/P game, you have to transfer it to a gen 5 game. Beating any of the games will unlock PokeTransfer. This is where you need multiple DS systems. Transfer the Pokemon from D/P to B/W/B2/W2. If you don't know how to do that, go here for instructions.
Finally, all you need to do is transfer the Mew from the generation 5 game to ORAS. You use Poke Transporter and Pokemon Bank for this (they're free to download but as I mentioned earlier there's an annual fee of just five dollars).
If you don't know how to do that, here are instructions.
And finally, you'll have Mew in ORAS.
Hope I helped!
