Raises, with reasonings (because I think explaining why a mon is better in the meta is helpful
Mega Sableye: UR (oops supposed to be a-) -> A+ -- This thing is a beast. Very hard to build around without using a charizard or a fairy, though admittedly people do quite a bit of the former. Versatile, can run taunt + wisp, CM, metal burst, and beat a lot of stuff. Quite a consistent mon too and imo defines stall in ORAS.
Mega Venusaur: a- -> a -- Like sab, this fatmon is so hard to build against. Great typing, huge raw bulk, great movepool (though imo maybe besides zard or sab it has the worst 4mss in 1v1 because of how much good stuff it can run) and anti-meta too. Charm rocks, and can help beat very popular mons like zardx and chomp. Can do stuff like beat kyub too which is epic.
mega alt: b+ -> a- -- This thing is SO anti-meta. It owns Gyara, both zard (very good in this meta),
Kyub, Dnite / dragons as a whole, Gren if you're spdef, etc. Also has an awesome movepool, and Cotton Guard and Confide both rock.
Azumarill: b -> a- -- Pretty big raise, but this thing deserves it - it's just so anti-meta, beating Gyara, both zards, kyub sometimes (what isn't sometimes vs kyub?) scarf pz, gren, etc. Being such a good blanket check vs a lot of dragons and special attackers rocks, but azu is really good when you consider its matchup vs high usage pokemon (ZARD, gren, etc). Great mon to build with.
Mew: b+ -> a- -- No brainer. Great, consistent stall mon, and stoss/amnesia can mess up a lot of matchups. Offensive is uncommon (though imo it has potential) but Kee berry + wisp is a mega consistent stall mon. Lower because it has to compete with sableye, and it loses hard to mega sableye.
Archeops: b- -> b -- I didn't personally agree and vote with this but I get it. Cool zard check and it's SO STRONG! Banded head smash is super nice for plowing through stuff like dragonite, meloetta, heatran, and you can also run stuff like switcheroo for chansey and outrage for garchomp.
Empoleon: b- -> b -- Another cool anti-meta mon. Water + steel is rad, and the matchups vs stuff like kyub, zardx, pz are just a few examples where water + steel proves to be really cool. Specs is awesome and yawn + whatever with torrent and peteya is pretty beast.
Terrakion c+ -> b- -- Anti-Meta mon. Destroying zard, pz, kyub, as well as being able to have a shot vs Gyara is just really cool in 2 slots with cc/edge. You can also use pjab to beat whims and double kick has a shot at beating zone while 100% beating pz (endure into hyper beam on a -1 spdef terrak can win). Has a pretty solid niche, if not being a little outclassed by TTar.
Clefable: c- -> c+ -- Not the most used mon ever, but ORAS really doesn't have a ton of good fairy types, but this is one of them. It gets Charm, CM, Amnesia, Encore (pretty underrated move), Twave, etc.
Mega Medicham: c+ -> b- -- I didn't vote for this either but this thing a) is super strong b) has good coverage and c) can be bulked if you want to.
Mega Gallade: c -> c+ -- You might think this mon's trash, then it beats your zard x. Bulk up is cool, and I always thought fighting types like Gallade had more potential than was used - fighting types can really be anti meta if they can beat zard and gyara, with a bonus of kyub too.
Volcarona: UR: -> c -- Great mon. Not only is it good vs steels, but it's also good vs a lot of fat stuff like psychics and venusaur and whatnot. Great vs stuff slower than it.
Toad's bulky set is super good, and helps vs faster stuff like lopunny too.
Serperior: UR -> c -- Really cool mon. AV has gotten good usage in 1v1pl, and can beat stuff like heatran too. Also really cool vs slow/fat stuff like slowbro and whims. Mirror Coat is super epic for sludge bomb venusaur, too.
Deoxys-Speed: d -> c- -- Deod got banned, so if you wanna use stall use this one I guess (you probably shouldn't, crit rate is too high, just use amnesia mew). Specs is neat though, and you might be able to pull off some NP + screens set.
Staraptor: UR -> d -- Intim is cool. So is featherdance and its stats. You can run defensive which is pretty cool (though I'd rather use cotton guard alt) or band.
Salamence: ur -> d -- Defensive is usable (though I haven't seen it) but scarf / custap are where it's at. Scarf Rock Slide is really cool vs zard and you can run superpower for PZ and stuff. Scarf outrage is really nice for a bunch of other dragons.
Vivillion: d -> c- -- Sure, it's outclassed by Jumpluff, but vivv is a lot more consistent. Beats grasses too. Not a D rank mon. If you don't need pluff's speed but need to beat slower fat mons try this thing.
Drops, with reasoning on some
Dragonite a+ -> a -- I don't think dnite is an A+ mon. I think band is super flawed - it has a ton of bad matchups vs stallish/fat mons like slowbro, venusaur, and Mega Sab, but it also isn't even that good vs the top ranked mons. It beats like, Zardy, Wispless Zardx, and scarf pz. But other than that this mon has too many bad matchups and flaws in general to be an a+ mon, including losing to rough skin chomp sometimes. I think it's goodish, but not a+. It isn't anti-meta and the bottom stuff can beat it easily too.
Mega Aggron a- -> b+ -- If you want a steel type that has a decent zard matchup, use heatran. Besides just having a generally huge defense stat, Mega Aggron doesn't really have that much of a niche that other steels like Mawile, Metagross, and Heatran can't do better.
Golem B+ -> B -- Study is cool and all but this thing is #1 pretty weak and #2 outclassed by uh, I don't know, Rhyperior, TTar, Terrakion, Archeops, etc. Has a pretty bad zard MU to boot, too, wisp / air slash blows.
Avalugg c -> c- -- i can't think of this thing's niche.
Cloyster c- -> ur -- bad mon
Mega Pige c -> d -- featherdance is a worse mega alt
Suicune c -> c- -- cool in bw but doesn't really have a good niche in ORAS, not to mention pretty awful matchups around the board vs the top mons in the meta/vr.
Mega Aero c- -> ur -- use a different rock type like terrakion or archeops
Mandibuzz c- -> d -- outclassed by msab in pretty much every way
Gliscor c- -> ur -- use landot for offense and some other mon like whims for stall
Sceptile-Mega c- -> ur -- woat grass type
Cincinno d -> ur -- use mega lop or something
Jellicent c -> d -- you'll almost always wish you were msab instead. cursed body is pretty rad though and saves this thing. you still struggle with fairies just as much as Msab does.
Machamp d -> ur -- use like conk