Figured I might as well go through the lower ranks as well, as a lot of things seem pretty inconsistent. Won't pictures cause I don't have time to get them unfortunately.
I'll quickly give a list of the things I'll discuss here, and then provide descriptions for each nomination afterword, I just felt writing down all the nominations would help so I don't have to continuously flick back to the viability rankings.
Seismatoad to B-
Infernape to B-
Mega Blastoise to C+
Entei to C+
Mega Latios to unranked
Shuckle to D/unlisted
Espeon to D
Pangoro to C+
Smeargle to D
Chandelure stays D
Cofagrigus to C
Haxorus stays D
Unrank the Following
Cloyster
Doublade
Exploud
Mienshao
Mega Glalie
Diancie
Seismatoad should rise because its a really reliable stealth rock setter, and water absorb allows to absorb the ever-so annoying scald. Its typing leaves it with only one weakness, and while not great offensively, it can spread burns and poisons with scald and toxic respectively, or even remove items with knock off. It can also check a ton of pokemon, such as Keldeo, Jirachi, Tyranitar and bisharp, while it counters Raikou and Manentric. Its a shaky check to most of these because its lack of recovery means it gets worn down easily, but if you need a reliable set rock setter that can act as a check to many common pokemon, look no further then seismatoad.
Infernape should rise because its a excellent mixed wall attacker that can actually be pretty difficult to wall, due to extensive movepool and unpredictability. Infernape is one of the few C rank pokemon that can fulfill multiple roles, such as a stealth rock lead, life orb mixed attacker, or even the incredibly underrated defensive set, which is can actually check a mons such as mega scizor, bisharp and weavile very nicely. As the the mixed set, it can blast open bulky pokemon with powerful stab close combats and fire blasts, while sporting excellent coverage in the likes of grass knot, hidden power ice, gunk shot, and stone edge. It even has access to priority to make up for its somewhat disappointing speed (seriously, how the hell does mega metagross outspeed this???).
Most of what I have to say about Mega Blastoise has all ready been said, but one of its biggest selling points is being a hazard remover thats not psychic or flying type, and not being weather reliant such as excadrill. Also not being pursuit weak is pretty sweet, which is the main reason starmie was denied a position in A+. Mega Blastoise, while slow, can really punch some holes in teams, due to its powerful coverage options, and its natural bulk allow it to take some hits, and retaliate with a devastating blow. All-Out-Attacker mega blastoise was something I used in X and Y, and it certainly hasn't lost is touch, meaning pokemon such as celebi can't switch in as easily.
Entei is a hidden gem, having access to one of the most spammable moves in the game, sacred fire, which as 50% chance to burn the target, turing pokemon that could normally switch into entei such as garchomp and tyranitar into unreliable and shaky switch ins. It also access to extreme speed to revenge killer pokemon such as talonflame after some prior damage. Whiles its movepool doesn't stretch much farther then that, iron head and bulldoze can be used to deal with mega diancie and heatran respectively. I could honestly see it in B- if it weren't for a crippling stealth rock weakness, as well as poor typing defensively. Also, charcoal + wisp is a cool set AM (not tagging cause apparently its a nuisance) incorporated in the team he created for me built around diancie and pangoro, which is able to lure in lots of threats and nullify them without having to rely on a 50% burn chance.
Mega Latios needs to get the hell out as soon as possible. The opportunity cost is simply to high. Why would you want to run it over other megas?
Yeah, buy running mega latios, you loose the ability to run president fluff here, and all his mega friends, such as metagross, loppuny, diancie, sableye, scizor, charizard and gyarados. As a special attacker, regular latios holding a life orb actually hits harder, and does not leave you unable to run another mega evolution. As a Dragon dancer, why use this over mega altaria, mega charizard x or mega gyarados? They all have better stab moves to abuse and are generally much more productive to either typing, abilitys, or better move pools. Even then, why not use mega latias, who is one of the most reliable checks to broken ass Landorus-I?
I subject thee to an eternity in hell!
Shuckle is also a horrid piece of work, sticky web was bad in X and Y, and borderline counter productive in ORAS. With two extremly common magic bouncers in the tier, as well as bisharp and serperior running a mock, shuckle will often be a liability, and its lack of offensive presence and recovery make it helpless to strong attacks, and it will eventually succumb to the onslaught. Since I'm an incredible rhymer, the vast majority of teams chuckle at shuckle.
Smeargle and Espeon are the literal definition of crap outside of uncompetitive geopass teams which is really common anyway, and can be stopped before it gets going if played wisely (though this is actually surprisingly difficult).
Pangoro is a personal favourite of mine, and its extremely underrated. It has access to 3 excellent abilitys, scrappy turning the would be counter sableye into bamboo for the panda, mold breaker being optimal on swords dance sets to beat clefable with gunk shot, and iron fist to get a more powerful drain punch and ice punch. Pandora, while deadweight against offensive teams, puts in a lot of work against stall, and can dent some balance builds as well. However, I think buffs pangoro to C+ rather then C is parting shot. This move allows pangoro to become an offensively oriented pivot, and circle around slower teams by forcing switches. The drop of offensive stats gives set up sweepers an easier time getting prepared to close the match, and for turning frail pokemon that struggle to set up into terrifying opponents. This has been nominated multiple times by various users so I thought I might as well throw in my support, because I have a lot of experience with this truly underrated pokemon.
Chandelure, while its nice is minute, it can be productive in certain situations. First, its a decent check to defensive altaria. Secondly, flash fire allows it to virtually counter mega charizard Y, a huge offensive threat. I also have found chandelure to be pretty effective against stall teams, walling clefable with out knock off/twave, beating mega sableye on a switch, energy balling quagsire, and taking a dump on the various psychics and grasses that are found of the most stall teams. I know its not much, but I think its enough to keep it D, at least for the time being. I don't feel too passionately for it, and I'll understand if it gets unranked, but I'd rather use it then a lot of the crap that resides it the lower ranks (looking at you mega latios).
Haxorus should stay ranked cause of the Swords Dance + Taunt set. Dragon dance sets are completely outclassed by the mega DDancers and dragonite, who isn't even a good Ddancer in the first place. Mold breaker allows to beat unaware pokemon and taunt magic bouncers. Once again, only really effective against stall and slower balance teams but enough to keep it ranked. Once again, its not that important and unranking it seems logistical, I just don't agree with the proposal.
Cofagrigus should rise because mummy essential screws over half the mega sweepers and wall breakers. It also has a mammoth defence stat backed up by moves such as willow wisp, toxic spikes, haze and pain split, and decent offensive presence in hex, and ghost is one of the best typing offensively due to the lack of pokemon that can deal with it. Cool on stall teams.
Just want to point out that having a niche doesn't make something viable. Their are ton of pokemon that can fit a extremely select teams and work, such as some of the pokemon show cased in CTC's team building compendium, which aren't viable choices, but can be made to work in extremely selective cases. Right now, the majority of the D rank fits this description. However, these are the really rotten eggs in my opinion:
Snobalts stated cloyters case, just a bad sweeper who gets hard stopped by waters and priority users and struggles to set up in the first place. Doublade is no longer a strong option for defensive teams as the've adapted to threats such as gardevoir and heracross with viable choices that do more then just check them such as jirachi and clefable. Cofagrigus or sableye are much better options for defensive ghosts. Exploud can only work on trick room teams and even then, trick room teams are limited for team slots as they must run two-three trick room setters and then other slow offensive pokemon, and while exploud fits this criteria, others such as emboar, azumaril, Mega Ampharos and even mega steelix are pokemon I generally find to much more worth a slot then exploud. Mienshao is pretty much outclassed by mega loppuny, while reckless life orb hits harder, loppuny's better speed tier, ability, and support movepool make it better choice, despite taking up a mega slot. Its not a atrocious pokemon, but it simply does not have a niche to ranked, and feels like a great example of a pokemon that fits only on extremely selective teams. I don't understand why anyone would want to use mega glalie over other mega evolutions. It has horrible defensive typing and stealth weakness make it difficult to switch in, and its mediocre defensive stats don't help its case either. Combine this with an undesirable speed tier and and slight case of the 4MSS as it has to pick between hitting heatran with earthquake or waters with freeze dry. In a metagame where mega titans rein supreme, glalie simply cannot compete. Diancie was only ranked cause its a reliable stealth rock setter and trick room setter, but as a fairy type, clefable is a better rocks setter, as it does not loose to the most common rock setter (Garchomp). Offensively, Mega Diancie is straight up outclasses it. Cressilia or cofagrigus are better trick room pokemon. Also, regarding the hipmotop nomination, I actually have used, and its terrible. If you are going to use it, at least use a set of close combat/rapid spin/foresight/toxic so it can spin against ghosts.
Anyway, thanks for reading (if you did) as this is a decently sized post. Goodnight everyone.