Hello all. It's been a while since I've battled. The last time I was on Showdown was probably May or June. Obviously I'm a little behind on what battling is like now. Would anybody be so kind as to give me a crash course in the major changes to the metagame that Gen 6 brought about? Just a list of "need-to-know" things is what I'm looking for, I guess.
There are a few Pokemon that you need answers for, otherwise they can destroy half of your team. The main ones are Mega Lucario, Talonflame, Aegislash, Bisharp, Mega Venusaur, Mega Mawile, Mega Pinsir and Mega Charizard X and Y.
A Ghost and Dark resist is important, as is a Flying resist. Defog / Rapid Spin are useful, as is a cleric. Sylveon is one of the best (don't use Florges, it's outclassed).
Mega Lucario can be either Swords Dance or Nasty Plot. It's usually Close Combat, Crunch, and Extremespeed/Bullet Punch for physical, and any three of Aura Sphere, Flash Cannon, Dark Pulse, and Vacuum Wave for special. Lucario is scary because there's no way to tell which one it is until the opponent plays it, but you can wall it; it just depends on the moveset.
Talonflame has been discussed already, but there are other sets you should watch out for too. Choice Band isn't the best, IMO. Sky Plate + Roost is good, and gives Talonflame much greater longevity. Swords Dance + Acrobatics can be hell to wall, as Talonflame takes no recoil damage from its main STAB. Bulk Up sets are specially defensive, and surprisingly tanky.
Recently, Talonflame is also being paired with Reckless Scarf Staraptor for an offensive double-dragon style offensive core. Lots of people use Rotom-W or Tyranitar to wall Talonflame, but Staraptor destroys these two with Double-Edge and Close Combat.
Bisharp is "the face of hyper offense" and hazard lead Deoxys-S' partner in crime. Defog lowers the opponent's evasiveness, which activates Bisharp's Defiant ability and gives it a free +2 Attack boost. STAB Sucker Punch, Iron Head, and Knock Off is not fun to deal with.
Knock Off was increased to 65 Base Power. The move's power is boosted by 1.5 when it knocks off an item. You'll see stuff like Assault Vest Conkeldurr making good use of this move.
Mega Venusaur is an incredibly potent tank. Its stats are 80 HP / 100 Attack / 120 Def / 123 SpA / 122 SpDef / 80 Speed. It's fast, incredibly bulky, and has great offensive stats. Giga Drain, Synthesis, and Leech Seed give it plentiful recovery, and Sludge Bomb is a great STAB for Fairies. It can also run EQ for Heatran, or Knock Off. The real kicker is Thick Fat though. MegaSaur is only weak to Flying and Psychic, and has plenty of useful resistances. Used correctly, MegaSaur is incredibly difficult to budge and some say that it's the only thing keeping Stall viable in this metagame.
Mega Mawile has base 105 Attack with Huge Power, which gives it the highest Attack stat in the game, surpassing even Choice Band Azumarill. Steel/Fairy is an excellent defensive typing, and Mawile is a slow, bulky tank that can be extremely difficult to play around. All Mawiles will have Play Rough and Sucker Punch, but the other two moves vary. Some run Swords Dance with Iron Head or Fire Fang. Some run SubSD, or SubSplit. Don't let it set up, because a +2 Sucker Punch OHKOs a frightening number of Pokemon.
Entry Hazards are slightly less prevalent this gen, mainly because of Defog; Spikes aren't worth the turns they take when the opponent can just use Defog, which can't be spinblocked. Stealth Rock and Defog are everywhere because of huge influx of SR weak mons that are worth the use and support. Main examples are Talonflame, Charizard, and Mega Pinsir.