I enjoyed the comical parts of this episode, and I get the feeling they were trying to do something with Zygarde/Squishy's conflict with Team Flare. I agree, that it really didn't go anywhere, or that it was just poorly executed.
Seeing Darkrai took me by surprise, and using it as a plot device to set in motion was obvious. I figured there were more than 1 Darkai at this point, as its been established there's been multiple legendary Pokemon. Not all, but a good number of them.
I got a kick out of the Pokemon talking, even if it was a tad cheesy and silly; but its a dream, can't give it high expectations.