Who doesn’t want to collect the Legendaries? The thing is, we’d all like to collect at some point (or rather, most of the time during gameplay), but then again you could be reluctant since you can’t get them without trading in Pokemon X and Y. Here’s what you can do if you’re interested in collecting Xerneas in Pokemon X, Yvetal in Pokemon Y, and do know that both versions will have access to Zygarde too.
Before you begin, do note that catching the legendaries are version-specific, so you’ll only be getting them based on the version you have. You should be expecting them in appearing all sorts of places, even in the same room inside Team Flare’s lab, so ensure to save beforehand rather than killing it.
The Xernea Legendary is a Fairy-type one, so it’s naturally weak to Poison and Steel and takes half damage from Fighting, Bug and Dark Type attacks. However, they are immune to Dragon. While Yvetal is a Dark/Flying-type Legendary, you should be expecting it to be weak towards Electric, Ice, Rock and Fairy, and that it takes half damage from Grass, Ghost and Dark-type attacks. It’s immune to Ground and Psychic.
If you’re interested in scavenging for the Zygarde as well, do know that you can do so at the Terminus Cave, because he will be found at the end of the cave. And more importantly, this Legendary isn’t version-specific, so you can locate him in both versions of Pokemon. But if all these are not sufficient for you, there’s always an alternative; trade it with either a friend or on the Global Trade Network.