The Eon Pokémon, Latios and Latias, are a legendary duo from the land of Hoenn. However, obtaining the legends will be a difficult task; perhaps even more difficult than roaming the entire region for a chance encounter in the original games.
The only way to catch Latios and Latias is to gain access to Southern Island via an Eon Ticket. But the only way to get the ticket is by attending Play! Pokémon events or using the 3DS StreetPass System. The former is simpler, just visit a location hosting the event and obtain it from one of the organizers. The latter might take a bit of time. You’ll have to StreetPass with somebody who has already obtained the ticket. You’ll activate it from one of the new features called BuzzNav.
It might not be worth it to go through all this just for those two. If you already have them on X and Y, just trade them over. Though, it might be worth trying to get as you’ll be able to traverse Hoenn’s skies atop one of the legends. Plus, they’ll be able to Mega Evolve and that’s always cool. There are only a couple of weeks left until we can check it all out.