The first trailer for the new anime season was just released for those that want to know more about it. One of the scenes briefly show Zygarde's 10% forme and Ash-Greninja in action. It's also confirmed that the Team Flare scientists will be making an appearance in the upcoming season.
As for my personal thoughts, I had a feeling beforehand that Zygarde's new form gimmick would involve the cells amassing together to create one giant Pokemon thanks to all the theories that have been brought forth when Zygarde Core and the silhouette of Zygarde's Complete Forme were first revealed. Now that it's all been officially revealed, I feel satisfied with the news. I like the concept, and I have a feeling Pokemon Z could involve some sort of scavenger hunt where you need to find a various Zygarde cells and cores to obtain the Complete Forme later on, or maybe Team Flare will also be after them just like you will and at some point in the game, they steal all of the Zygarde cells and cores you collected to further advance their plans of summoning Zygarde's Complete Forme on their own.
When I first saw Zygarde's new forms at first, I found them a bit odd at first considering they weren't the designs expected. I thought the Complete Forme was still going to retain the snake-like form, and I was also very shocked that we had another completely new form. he more I look at them, however, the more the designs are growing on me in a good way. Zygarde's 10% Forme looks like a Pokemon that could be in my top 100 favorite Pokemon thanks to its design, and the Complete Forme has a sort of "ruler of the earth" design that seems pretty fitting considering it monitors the ecosystems.
As for the Ash-Greninja, I don't mind it at all. In fact, I actually like the black coloring coming out of its ears and the red hue on the top of its head. I originally thought this was going to be Greninja's Mega Evolution (which wouldn't be too surprising since it would be a great idea to give Kalos Pokemon Mega Evolutions with the newest games), though after I read its official English description (which you can read below), I don't think it may be the case.
Ash’s Greninja takes on a mysterious new appearance in the latest season! Ash-Greninja is the form that Greninja takes when the bond between it and Ash is raised to the limit. The strength of their bond changes Greninja’s appearance, and it takes on the characteristic look of Ash’s attire. This phenomenon is also said to have happened just once several hundred years ago in the Kalos region, but it remains shrouded in mystery.
I remember reading a comment on another Pokemon forum that suggested the Ash-Greninja phenomenon could actually be similar to AZ's Floette, especially when you learn Greninja assumes this form when its "
bond between it and Ash is raised to the limit" and such a phenomenon is "
said to have happened just once several hundred years ago in the Kalos region." When you look at AZ's Floette, it does look a lot different from other Floettes since it has a completely different flower and its color scheme is different. In fact, the color scheme on AZ's Floette matches the AZ's clothing when he was the Kalos King (going off the dark coloring), and considering the two share a very close relationship, perhaps this Ash-Greninja phenomena happened between AZ and his Floette as well.
It's even worth noting that about a month ago, Pokemon's marketing director gave the cryptic message "flowers" to hint at Pokemon's future when interviewed by Nintendo World Report, so there's no doubt more information about AZ's Floette will be revealed in Z (and perhaps even in the anime). This is all just speculation and it could end up becoming false, but I thought I'd provide these ideas as food for thought. I do hope that Greninja won't be the only one that will have this form change treatment though.
As for the anime itself, I'm definitely looking forward to it, though the inclusion of the Team Flare scientists is giving me thoughts that Pokemon Z may not be a sequel. I mean, I'm pretty sure the scientists are finished with Lysandre's supposed downfall, at least if Xerosic is anything to go by. I'm curious to see what will Team Flare's leadership be like in the upcoming game.
I'm personally hoping Z will be a sequel though. I mean, I don't see Team Flare using Zygarde to fuel the ultimate weapon, and if the anime is anything to go by, it looks Team Flare will use Zygarde for something else that we will only understand over the coming months.