Terrakion, Mega Heracross, Mega Medicham, and Mega Gardevoir: Aegislash getting banned was a blessing for those four, and with its absence there is no denying how strong and influential Pokemon they are. Everyone agrees with this, so i won't explain anything else here.
Mega Scizor: Mega Scizor is an excellent Pokemon but it finds it hard to sweep in this metagame, so it prefers taking defensive and utility roles, such as checking offensive Pokemon with Bullet Punch, pivoting with U-turn, providing utility with Defog, and checking physical attackers. Those roles are great and all, but Mega Scizor is not threatening enough to be in A+, which causes it to be taken advantage by some really dangerous Pokemon such as Mega Charizard X and Y, Keldeo, Thundurus, Mega Mawile, Mega Gyarados, and Talonflame.
Tyranitar: Check CBB's post which is quoted in this page by TRC.
Mandibuzz: Mandibuzz struggles with the new offensive threats that are becoming popular, namely Terrakion, Mega Heracross, and Mega Gardevoir, meaning that it's becoming a bit less relevant as a defensive threat. However, it still handles quite a big number of dangerous Pokemon (Landorus, Garchomp, Talonflame, Excadrill, Mega Scizor, regular Gyarados, DD Mega Charizard X, Dragonite, and Breloom), and provides lots of utility with Defog, Taunt, Knock Off, and Toxic, which is why it didn't drop in B+.
Mew: Excellent stallbreaker, excellent Defog user, very hard to kill, fast enough to keep up with offensive monsters such as Mega Heracross, few exploitable weaknesses, what else do you want me to say? You all agree anyway, so just go on to the next Pokemon.
Amoonguss: With the resurgence of the three offensive Megas that Aegislash held back (Medi, Garde, Hera), giving up your Mega slot on Mega Venusaur is not always easy, so Amoonguss is here to fill this gap. It deals with the two most threatening Water-types in OU, Keldeo and Azumarill, has Spore and Stun Spore to make it somewhat threatening, has good all around bulk and a great defensive typing, and it never dies thanks to Regenerator. This means that it can reliably check many big threats such as Thundurus, Mega Gyarados, Rotom-W, Gengar, Terrakion, Gliscor (With HP Ice), and Breloom, and has become one of the premiere defensive Grass-type of XY OU.
Slowbro: Terrakion counter? Check. Mega Medicham counter? Check. Mega Charizard X counter? Check. Hidden Power Grass-less Greninja counter? Check. Anyway, you get the drill, Slowbro walls like half the Pokemon out of S and A rank atm, is not easy to take advantage of thanks to access to three kind of status moves and a decent SpA stat, and never dies thanks to Regenerator and Slack Off. Definitely one of the best defensive Water-types in the metagame.
Alomomola: I know it's getting repetitive to talk about the same Pokemon in each update, but bear with me :D. Alomomola slowly but steadily has proved how good of a Wish passer it is, keeping healthy a ton of good defensive Pokemon that lack recovery, such as Heatran, Tyranitar, Mega Ampharos, Chesnaught, Rhyperior, and Victini. It also has double status to make the opponent think twice before switching in, as well as Regenerator to allow it to focus on healing its teammates instead of itself. It also checks a lot of stuff, and even though set up sweepers are its bane, there are plenty of defensive and offensive Pokemon that pair well with Alomomola and can deal with those.
Conkeldurr: Now that the hype about Assault Vest Conk has died down, the ugly truth has started revealing: Conkeldurr is not a great, or even a good Pokemon, it's just ok. It lacks recovery and thus gets worn down very fast, its slow as ass and almost always needs to take a hit first except when facing Pokemon weak to Mach Punch, is easy to wall with threatening MEvos being everywhere, and in top of this three MEvos that can take advantage of Conkeldurr easily have risen in usage and viability over the last weeks, namely Mega Medicham, Mega Gardevoir, and Mega Heracross, all of which can switch with relative ease into Conkeldurr and take advantage of it.
Gothitelle: Gothitelle is an ok Pokemon, but it's kinda niche for B. It provides no defensive synergy on a team, which puts a big strain on teambuilding and shows that you can't just slap Gothitelle on a team and call it a day. Also, there are a lot of scary wallbreakers that are able to fuck up stall teams, so Gothitelle lost one of her previous roles. Her main function is partnering up with sweepers and removing their counters, which is good enough for B-, but too one sided for B.
Zapdos: Zapdos doesn't like the effects that Aegislash's absence from the metagame has had. Terrakion, Mega Gardevoir, and Mega Heracross are all Pokemon that scare Zapdos shitless, and even though Zapdos is a good check to birdspam teams that have started becoming a bit more popular, her worse performance against almost any other kind of offensive team means it's not B+ material anymore.
Magnezone: Magnezone can trap almost any Steel-type for a team, can outspeed and check many offensive Pokemon with a Scarf set (Keldeo, Terrakion, Talonflame, Mega Pinsir, Mega Gardevoir, Dragonite, Landorus, Garchomp (you need HP Ice for the last three)), has Volt Switch to keep momentum even when it's choiced, and has great bulk and resistances to even switch into some of the Pokemon it wants to trap or revenge kill. It's reliable and a great offensive support Pokemon that deserves to be in B rank.
Sylveon: Mostly outclassed by Clefable outside of a strong Hyper Voice and the ability to use a Specs set, which is why it's falling to C+ and not any lower.
Jirachi: Can check / counter Greninja, Clefable, Latios, Latias, Mega Gardevoir, Thundurus, Mega Venusaur, Kyurem-B, Mega Alakazam, and a few other threats, has useful stuff to do against the Pokemon it walls, such as passing Wishes or spreading status, and also has a very decent Scarf set. C is good for it for now, it may rise a bit higher in the future.
Cresselia: Some people have compared it to Mew, and fairly so. However, Cresselia has a few things over it: huge bulk, Levitate (which lets it counter Pokemon that Mew can't, such as Excadrill and Garchomp), and Lunar Dance (a great way to support sweepers). Those three traits make Cresselia C+ rank worthy, as it's quite a useful Pokemon on defensive teams for its ability to handle a plethora of dangerous Pokemon, while also being able to fit on some bulky offense teams thanks to Lunar Dance.
Haxorus, Salamence, and Zygarde: Mostly outclassed Dragon-types that have no use in OU outside of some very niche roles on DragMag teams.
Sableye: One of stall's few counters to Mega Medicham, great stallbreaker that also beats some dangerous stallbreakers such as Gengar and Mew.
Hawlucha: Aegislash leaves from OU and Hawulucha becomes much more viable, as it's now able to clean up much easier against all kinds of teams. Yes it needs support in order to set up and because priority users hurt it, but not that much support to put it in the same rank as way more situational Pokemon such as Ludicolo, Tornadus, and Dugtrio.
Sharpedo: I don't even know why someone would want to use Sharpedo, so i am putting it in D rank for now just to give some time to anyone that wants me to keep it ranked to provide a proper explanation as to why i should keep it ranked.
Victini: Mega Medicham and Mega Gardevoir hard check is crazy good for stall and defensive teams in general, TauntWoW is a really cool set. It also helps that it has great synergy with most Wish passers, such as Clefable, Alomomola, and Chansey. Finally, it's offensive sets are cool too, especially a recent innovation i have been hearing about, SubPuP with V-Create and Bolt Strike.
Omastar: Better than most C rank stuff mostly, it's hard to fit on rain teams but its combination of power and Speed under rain is absurd, not to mention that you hardly need any prediction when using (just a lucky charm because fuck Hydro Pump).
Toxicroak: Niche rain mon similarly to Torn-I, also can be used on offensive teams that struggle with a lot of popular mons, such as Keldeo, Azumarill, Terrakion, Clefable, Suicune, Alomomola, and Breloom. It's also not that easy to wall with Aegislash gone, so Drain Punch + Gunk Shot / Ice Punch + Sucker Punch is great coverage.
Granbull: Good Mega Medicham and Mega Heracross check that also checks a lot of physical Pokemon and has a decent amount of support options, such as Heal Bell, Thunder Wave, and Roar. Also hits hard enough to beat a lot of the Pokemon it checks.
