I agree with what PlatinumDude said, you're not providing enough information. All you've done is provide the names of Pokemon and that's it. That doesn't tell us anything because a Pokemon can run several diverse movesets (for example, Celesteela). Also, as said, what format are you playing in? From the looks of things it appears to be Ubers because you've got Shaymin-Sky, but your team choices seem to justify against that (for example, Leafeon).
I'm going to have to be blunt here, even if you provide more information about the Pokemon, this is not a team. It's literally just a bunch of 6 random Pokemon put together in the hopes that they will work. What I would do is take one Pokemon and build the team around it, or maybe use a well-established "core" - that is two or three Pokemon known to work together, and base your team on that.
I know that Suicune, Shaymin and Lunala work well together, but what should I replace the zygarde with?
But the Leafeon is special.
You should consider replacing Zygarde-10% with its 50% forme or even its 100% forme. As was said before, Zygarde-10% has lacklustre stats and a rather shallow movepool, and in its role is outclassed by 50% forme. The 100% forme, on the other hand is used more as a physical wall that rocks Rest and Sleep Talk. And how is the Leafeon special?
Okay, I'll try using the complete form of zygarde. The leafeon is special to me because I have used it to defeat the elite four on every game I have played. If I did replace it, though, would Virizion work?
I was personally thinking Serperior. It can rack up Special Attack boosts with Leaf Storm.
You should consider replacing Zygarde-10% with its 50% forme or even its 100% forme. As was said before, Zygarde-10% has lacklustre stats and a rather shallow movepool, and in its role is outclassed by 50% forme. The 100% forme, on the other hand is used more as a physical wall that rocks Rest and Sleep Talk. And how is the Leafeon special?