I'm not sure if this has been mentioned yet, but my friend and I discovered something interesting last night.
I went and used a Mega-Banette against my friend in battle, giving it a test. On the turn iI evolved it into it's Mega form, I chose to use Substitute as well. Now as we know, Prankster kicks in on it's evolution, and takes effect immediately. Sadly, that wasn't the case for my poor ghost pokemon, as he ate a Toxic before the substitute could even come out.
Sure enough, the -next- turn, Mega-Banette went first, but on the turn of it's Mega-evolution, it went second.
So my friend and I took a controlled enviroment, tested it again with a speedy pokemon of his, used surf on the same turn I evolved and through out a thunder wave, and sure enough, he went first again.
Curious, we tested other Mega's, who's ability -did- take effect on the same turn they evolved.
I'm calling program error here in the turn order that Game Freak must have overlooked and should be informed to patch in the future, because there's no reason Banette -who's already had years of misfortune in NU- should get a Mega that doesn't work properly.
Sure, I can throw protect out on that first turn of evolution, but I shouldn't have to. xP
Anyway! I just wanted to throw this out there if no one noticed it.