Based on the current info we have, plus the fact that we don't get a glimpse of Ash-Greninja makes me wonder about a couple of things.
One, both Ash and Greninja are wearing their battle pulse bracelets, but we don't see even a glimpse of Greninja transforming. Why? He did so last time against Sceptile, what makes this any different?
Answer: The risk. Ash doesn't seem to care too much about taking the after effect of fainting during battle, but I'm sure Greninja doesn't want that for his trainer. This is going to lead up to the inevitable 'conflict' between these two. Ash thinks Greninja is trying to do his own thing, while he's really just trying to avoid overexerting his trainer.
Second thing here is Ash losing. Yes, he's going to lose. It's obvious at this point that Sawyer has done a great deal of training since he last met up with Ash, especially with getting the Psychic, Fairy, and Iceberg badges. So with the 3-on-3 setup we have, it's no surprise that he has the clear advantage, both in typing and strength. But the big factor that I believe will make Ash lose all three battles is the fact that Greninja won't transform.
Aside from that, nice to see Xerosic doing something interesting here. Tensions for the final battle are steadily rising, and I can't wait!