Spore got nerfed along with Sleep Powder with Grass being immune to both (which is funny, considering Grass-types are the ones that use Spore), so I expect more Dark Voids and Lovely Kisses for sleeping. Also, Water Shuriken is going to be great. Some notable threats I see using it are Azumarril, Cloyster, Crawdaunt, Basculin, and maybe Gyarados. In other news, Frost Breath becomes an alternative STAB for Ice-types (crits are 1.5x and Frost Breath is now 60 BP, making it 90. That ties with Ice Beam, which has been nerfed to 90 as well). While it can't freeze or "crit" like Ice Beam can, it does bypass SpDef boosts. Also, Geomancy is scary, although it needs Power Herb to be any good imo, which could be a huge drawback. Gardevoir is probably the best Geomancer, since it can hit Blissey with Psystrike. Also, Sticky Web is going to be interesting, especially since all Bug-types get it. Illumise / Volbeat get prankster on it too, so that'll be fun.
Speaking of new pokemon, Pyroar and Talonflame could be threatening, both with Shell Smash. Alternatively, Pyroar can run Boomblast, but I think Shell Smash is probably better on it. Talonflame is going to be fun though. Heliolisk is in the same boat as Pyroar. Intrestingly, Dragagle gets all Water-type moves from Skrelp, although Water doesn't give it much to be honest. A neat pokemon is Greninja, who has a really fast Dark Void and good neutral STAB combo between Water and Dark. It's power isn't the strongest though, which could be a problem, but it does have a really fast Water Spout (if PS! is correct, it has the fastest Water Spout without any stat modifiers at 120). Delphox can go pseudo-mixed with Psystrike and Blue Flare. Pretty much a better special victini; not much else to say, really. Chesnaught gets the grass package of Spore and all of the stronk Grass STABs. The best Grass STAB for it is probably Horn Leech though, for that extra recovery. Funnily enough, it also get Drain Punch, meaning both it's STABs can heal it. This is pretty neat on such a bulky monster, especially since it doesn't look like it gets a recovery move. It also has immunity to Spore and other powder moves, which is neat. Also, it can run a phazing set with Storm Throw. Pretty neat.
In the Megavolution area, Mawile is looking really threatening with Shift Gear. Normal Mawile intimidates and sets up with it's good bulk, and then pops a Megavolution and sweeps with it's +2 Speed and +1 Attack. It's not weak to priority (although it doesn't resist it either) and has decent enough bulk. Mawile is going to be fun. Megachomp's DD is going to be crazy. It'll be like DD Kyu-B, except without the shitty Ice-typing. It does lose some bulk though. What's interesting is that Garchomp can pull a pseudo-Double Dance set with it's Megavolution. Against offensive teams that outspeed MegaGarchomp deal with normal Garchomp, as Garchomp probably won't need the extra power. However, against bulkier teams, MegaChomp can rip things to shreads with base 170 attack. It loses a boosting item though, so not sure how good this will be.
There's definitely a ton of shit I missed, but that's what I'm thinking at the moment.