Junior Tycon, I already have a shiny Mega Latios and shiny Mega Latias in Y!
Latias is slightly smaller and has different coloured eyes. Apart from that they're identical appearance-wise. They get different stat boosts.
They're available via Datel Powersaves, so it's kind of cheating. My friend got one and gave me the Mega Stones. I only use it with friends though, so I don't think I'm cheating, especially when people battle with Volcanion, Hoopa, Diancie, and eggs now
Not a big fan of the three new Mega Evolutions, but they're not terrible either. Competitively, they sound like they're going to be absolute monsters! Sableye's still my favourite new Mega Evolution though
I'm hoping for Mega Flygon still.