Mega-Kanga is crazy. Period. If it's running Fake-Out in doubles for weaker Pokemon that's half their health gone in a hit, same for singles. Power Up Punch on this thing is verging of broken. Return, after a PuP in particular, is crazy powerful. I like using Impish 252/hp 176/def Gliscor and after PuP is blew through me in 1 (count it) 1 hit with Return! I was in shock. Only thing it seems really weak to is Ferrothorn holding a rugged helmet. At least I thought that until I meet one who had Fire Punch. Thing is unpredictable and should never be taken lightly.
In a similar vane is Mega-Pinsir. Sporting a whooping 155 base atk, dude will wreck shop if it gets a swords dance online. Worse still, its ability turns all its normal moves into the flying type, so quick attack becomes a solid priority move. If Pinsir comes in against a weakened team that's pretty much it right there. Talonflame seems like one of the few things that stop it at that point.
The large amount of setup sweepers is amazing. I remember in gen 4 when a team was happy to get one boost and struggle to a win from there. Now every poke and its mom has some boosting move that will destroy your team unless you're careful. Quiver Dance, Shell Smash, Lucario getting a Nasty Plot or Swords Dance, Kanga getting off a Power Up Punch, Pinsir getting of a Swords Dance, Aegislash getting off a Swords Dance, Swords Dance in general, Dragon Dance, Tail Glow, etc. What's worse is the baton passers like Scolipede and Smeargle that can make even the cutest Pokemon a terror. Lost to a baton pass team using Clafable as the recipient. The rest of my team had already been exhausted, and after a few Cosmic Powers in addition to the boost it receive the thing was impossible to take down.
Ghost type is new best type. Losing the steel resist was huge. I've seen Aegislash spam Shadow Ball because there isn't much you can do about it anymore. Dark isn't known as the type for powerful walls, and Normal is Normal.
Misses from moves are more costly than ever. Miss a Toxic on that Kanga? You lose. Couldn't burn that Aegislash? You lose. Focus Blast miss your target? Now you get swept. This point goes hand in hand with the above. Sweepers are just so destructive in this meta.
Which leads to my final point: stall is dead. While some might argue it was dead a long time ago, it's absolutely true now.
Thanks for reading this rant and if there are any things you guys have noticed about the current PvP formats or any Pokes you find OP/weaker than before let me know!