[spoil]Assuming my supposition is correct, I don't know. Talonflame obviously has access to boosting moves (swords dance, bulk up), but other than that it has a pretty mediocre attack. Ash-Greninja will definitely outspeed Talonflame, and have much better attack, and let's not forget it can still run an item like Mega-Rayquaza - which is litterally what sent Mega-Ray outside of Ubers. (Item combined with +100 BST boost - and for all we know, Greninja's boost could be higher, considering it appears Zygarde itself likely gets more than +100 due to its insane HP boost - something I've discussed when Z100% was confirmed to be in Sun and Moon).
Other possibilities with Ash-Greninja is that Water Shuriken changes when it changes form - not just an increase in BP. It could become a double hitting priority move with 50 BP for each hit, like Gear Grind or Bonemerang. Or it could get +2 priority. Although I think just the sheer power will change.
One big advantage this has over priority Brave Bird is also that it doesn't cause any recoil damage, can break through substitutes and can break through focus sash/sturdy.
Finally, I really do like to think Ash-Greninja will get a unique Z-move - something like that big shuriken it used in the finals in the animé. This could also be a priority move with very high base power, if true.
Of course we will have to wait until we can affirm that Talonflame will be more threatening. If only Battle Bond was the ability of just base Greninja, and Ash-Greninja got an ability like Skill Link
That said, Ash-Greninja appears to be more of a demo-exclusive gimmick, so I actually would be surprised if it got a unique z-move.[/spoil]
