Yveltal, a f*cking legendary bird of death (Jur Meeuws)
Get it? It's a giant evil bird that looks like a Y, because it's hand-wings and hand-tail (or...possibly hand-genitals, tough to say) form a Y. It's actually a little more terrifying than you'd think - according to its Pokedex entry, when it dies it absorbs ALL OF THE LIFE ENERGY IN THE UNIVERSE - then it goes into a cocoon and the universe is presumably reborn. So, ya know, feel free to teach it 'Cut' and use it as an HM slave or something so you never have to use it in battle and risk it dying/destroying the universe.
Tyrantrum #1 for me, it's a motherfucking T-Rex after all (Craig Stark Forsdike)
The biggest question I have about Tyrantrum is "How?" As in - "How did they not do a badass T-Rex Pokemon so much earlier?" I mean, it's a T-Rex Pokemon. Of course it's amazing. This is the dream that was born when we all saw Jurassic Park - a huge, powerful T-Rex that we can control. Suddenly, it's like you're John Hammond - but instead of getting your grandkids nearly eaten, you're stomping out puny raptors and anything else that gets in your way all by yourself.
Greninja, of course. Who wouldn't love a badass ninja frog who uses his tongue as a scarf!? (Andrew Wilson)
The greatest Pokemon of X & Y is, naturally, the ninja frog who uses his tongue as a scarf (thanks other Andrew, hard to come up with a better description than that). One of the great things about all of the starters from this generation is that the final forms are almost nothing like what you would have expected them to be: adorable Chespin becomes a tank, cute little Fennekin becomes a wizard-monk, and confused Froakie becomes a badass ninja constantly tasting its own neck.
Plus, it has a move where it creates shurikens out of water. As much as we all dreamed of having a T-Rex when we were kids, we all wanted to be ninjas. And, sadly, this is the closest most of us will ever come to achieving that dream.
Still, it's better than becoming a fairy keyring (who's actually pretty good, by the way).