Hydreigon: Cool Wallbreaker, has extreme offensive stats backed by a respectable base 90 speed, but that x4 Fairy weakness is cringeworthy, and is walled to hell and back by Azumarill. I want to say C+ Rank.
Then switch out? Honestly, Fairy is not the end of the world, Tyranitar has a 4x weakness to Fighting, yet it's still amazing, 4x weakness ≠ bad. You want to say C+ Rank, but try out Specs Hydreigon, it's very powerful.
Gothitelle: Great Specs user with access to trick and various status moves and the amazing Shadow Tag. I'd give it B Rank.
Cresselia: Arguably the best wall in the whole game. It can boost its mediocre offensive stats with Calm Mind, and has Moonlight for recovery and the awesome Healing Wish for Utility. I'd give it A- Rank.
You mean Lunar Dance, I hope. Cresselia is shut down by Taunt and Toxic, and as much as I love it, it has a prety bad typing, and Calm Mind sets are only good in RU, and while it is bulkier, I don't think it is deserving of A-, B-, however, seems reasonable.
Durant: Great typing with only one weakness. Truant + Entertainment is hilarious, and Hustle + Hone Claws is cool too. Meh, B+ Rank.
There is no way in hell it is B+, it is C at best, it is super frail on the Special side and is shut down by faster threats such as Talonflame, not to mention Truant is the gimmickiest thing ever. Try using it at the higher ladder, the results aren't that good. Try to actually put more thought than one good point, then just a rank.
Haxorus: This thing was a beast before the introduction of Fairies, packing an amazing 147 Base Attack Outrage. Poison Jab can counter back I guess, but it lacks great bulk. C+ Rank.
Meh, it is good imo, but C+ just seems so low, however I'd say it is fine here.
Tornadus: The least used of its trio, Tornadus has good traits including Prankster (Prankster Taunt what), awesome offensive capabilities, and a respectable typing. However, its lack of good movepool hurts. C Rank.
Its lack of good movepool? Hurricane, Taunt, U-Turn, Superpower, Heat Wave, amongst other shit is not a lack of movepool. Do you seriously believe that? Honestly it seems like you lack experience with Tornadus.
Toxicroak: This pokemon was much more usable when Rain was being spammed everywhere (it's now RU :[) but it still has good attack and speed. Nasty Plot can be used for a surprise set and Black Sludge is nicely paired with Dry Skin. D Rank.
RU ≠ Less OU viability. And why the fuck are you using NP? Run SD or bust. Gunk Shot got a nice buff this generation and it can actually beat Aegislash. I'd think it would be C Rank, as it is very powerful at +2, however it lacks Speed and bulk, along with not the best typing.
Zoroark: This is an awesome pokemon. Team preview fucks its ability up a bit, but a Dark Pulse coming from a Mega Venusaur is pretty cool. An awesome movepool with Flamethrower, Nasty Plot, and Dark Pulse is really diverse. However, its terrible defensive capabilities even it out a bit, and fairies didn't really help it. B- Rank.
No, Zoroark is C+ in my book. It may be strong, but after it's been given away (not that hard), its uses decrease tremendously. The better set is mixed Life Orb, which can actually do something.
Umbreon: Always a really annoying pokemon with wish and foul play, Umbreon's amazing Defenses and High HP make this thing a complete wall. Wish + Protect is annoying as hell too. A- Rank.
Umbron is utter shit in my opinion, but I guess there are way good points, but it is nowhere near A-, fine where it is really.
Venusaur: This thing would be awesome with Zard-Y. A Chlorophyll sweeping set with Growth is terrifying. Too bad it has a limited movepool. B- Rank.
Sleep Powder, Giga Drain, Sludge Bomb, Weather Ball, Growth, Swords Dance, Earthquake are just a few, not a bad movepool imo. Stop saying they have limited movepools before you actually explore them.
Barbaracle: Shell Smash, Razor Shell, and Cross Chop are this things gems. A x4 weakness to grass is totally amazeballs, but it has nice physical defense as well. It has cool coverage, but is outclassed by other pokemon. C- Rank.
Fine here.
Reuniclus: Magic Guard + Life Orb + AMAZING BULK is terrifying. Calm Mind and Psyshock are its main gems. Focus Blast is good for Dark Types. It can also take most hits well. A Rank.
It is NOT anywhere near A Rank, at best it is B for huge weakness to Aegislash and Taunt and is just not what it once was, good Pokemon, but not that good.
Amoonguss: This is a good wall. 114 Base HP with OK 85 offensive Capabilites. Spore is awesome, and Clear Smog fucks Azumarill up. It has good typing too, but pretty slow speed. C+ Rank
Don't use offensive top fucking lel, and Speed doesn't matter. I think it should be C, but either are fine.
Milotic: It's a good wall with offensive capabilities and good typing. Competitive screws Defog and Sticky Web over. It has a shitty movepool though. C- Rank.
Here you say shitty movepool, but Recover, Scald, Ice Beam, Dragon Tail, Haze, etc... Stop.
Exploud: Boomburst. That's all. C Rank.
Exploud is shit honestly, more like C-.
Gorebyss: It has Shell Smash and Baton Pass. So I guess it's OK. C- Rank.
Meh.
Omastar: Awesome special attack with Shell Smash is really good. B+ Rank.
Meh :/.
Shuckle: The premium wall. It has bad everything else though. C Rank.
Meh ://.
Hawlucha: It's so outclassed by everything else. D Rank.
How is it outclassed? What else gets Unburden + SD + High Jump Kick? It's really fucking strong and fast at +2/+2, it's like a Shell Smash without Defense loss. It is certainly C+ or B- if you ask me.