I'm not really worried, just because why should we need to know at this moment if the fire shuriken hits Charizard X if the preview showed that then there's goes all the tension behind this mysterious attack and what I want to know is what happens before Ash and Greninja bring out this power, like are there going to be flashbacks showcasing everything Ash has been through with his pokemon leading up to this moment I mean it would put a lot of meaning behind this attack.
I mean no matter Ash isn't just trying to win this league for himself, he's trying to win this for his pokemon, friends, his mom, practically for every single trainer who wasn't able to make it to the league being entrusted with all their hopes and dreams. He's giving it his all and I would expect nothing less from Ash at this point.
The only thing I'm worried about is the day the episode airs someone is going to spoil the result destroying all the hype this episode will have, so hopefully no one spoils the episode, anyway Ash finally deserves to have his win over Alain and what better place to do it than at the kalos league finals! Since the idea of a rematch against these two won't be happening.