Alexwolf wanted actual "substance". *Skip this post if you have knowledge of the metagame*
Tornadus C ->
D/Unranked
From what I've seen, there are two types of viable Rain teams: the offensive ones that only utilize Politoed for Rain and the Hyper Offensive teams that use Politoed + another dedicated Rain Dance user (these stack Swift Swim Pokemon). Okay, now why the heck would you use Tornadus over its Therian forme or Deoxys-S for setting Rain? Sure it has prankster, but its already fast enough to set it up without much difficulty and if bulk is a problem then you can just use Tornadus-T, which sticks around much longer thanks to Regenerator and can actually switch into attacks. Tornadus just screams completely outclassed, so much so that I don't understand why it has an analysis.
Mega Aggron C+ ->
C
I'm just going to use other C+ mons for comparison: There's Entei, Klefki, Krookodile, Shuckle, Haxorus.. Aggron is just not as viable as any of them. Why? It checks/counters some pretty big mons like Pinsir, Mawile, and many others that aren't worth mentioning, because plenty of other Pokemon can wall them too. Now, lets get down to why it isn't good. Aggon has no means of reliable recovery, the attacks it uses makes it walled by just so many common OU Pokemon (gives up too many free turns), especially if not running an Offensive team, and there are other Pokemon that can wall most of the Pokemon that Aggron can cover. There's just too big an opportunity cost that comes with Aggron too (also takes up a Mega slot, preventing you from running the other, better Megas).
Kyurem C- ->
D/Unranked
Kyurem's in the same boat as Tornadus, there's seriously no real reason to use it. Of all the stall breakers viable in OU, why use Kyurem? It isn't a good breaker this gen. and there's plenty of stall teams that can outright deal with it and then it is borderline useless against offensive teams. It doesn't have its brother's offensive presence, meaning there's just a lot of things that can switch in without taking too much damage and force it out. Kyurem's also pretty weak to hazards and doesn't threaten its setters enough.
tl;dr: No justifiable reason to use this over Landorus-i, Kyurem-Black, Gengar, Suicune, etc. for stall breaking or whatever you are trying to use it for.
Gourgeist-XL C ->
Unranked
Its analysis is rejected, its completely outclassed by Gourgeist-Small, and on top of that, it doesn't fit into the metagame.
See this post for more details. I'm not going to rehash what's already been said.
Abomasnow (-Mega) ->
D/Unranked
"With Abomasnow gaining a Mega Evolution this generation, Mega Abomasnow manages to be one of the best wallbreakers to use with its access to a powerful Blizzard." That's from the analysis. Abomasnow can't even do that properly, it's hardcountered by common stall Pokemon like Chansey, Special Defensive Skarmory, Mega Scizor, and Aegislash. More things to add: Abomasnow's weaknesses are also too common for it to properly switch in, Mamoswine is a better user of Ice Shard, extremely slow and gets outsped and damaged by nearly the entire tier, its ability is pretty much useless this generation (for OU), and it takes up a Mega slot that could be used for something good. Its pretty much Kyurem, but far worse... -_-
Moltres ->
D/Unranked
Picture Talonflame without anything that makes it good, here it is, Moltres! This thing was usable and not that bad when Mega Lucario and Genesect were in the tier, but they aren't anymore. Its analysis has some SubToxic set that gets walled by many Pokemon and has even more switch ins. I have yet to see even an average player use Moltres. It just doesn't fit the metagame, what's not to get?
Snorlax ->
D/Unranked
Snorlax has been promoted as a Charizard Y switch in, but it comes with sacrificing reliable recovery and still has the same issue as Chansey: It's screwed over by Pursuit. One could also use Goodra, which is still more effective than Snorlax. The teams Snorlax fits in to are few and far between, while still not being the best. And it has competition for its very niche role. Snorlax is cool and all, but it just isn't worth listing.
Blissey ->
D/Unranked
Just read the thread.
Something else to add is that its main move, Flamethrower, isn't as useful as it was last generation, where you can speed creep CB Scizor and net a surprise KO. Normal Scizor is no longer common and instead you have to deal with its much faster Mega.
Shuckle
Shuckle is better than every other C+ Pokemon and most mons in B-, but I'm fine with it staying here, because of the posts in the Ubers viability thread. Sticky Web is in itself niche and you have to dedicate an entire team around it for it to be worth using. Sticky Web is also less effective than it is in Ubers - because of the metagame right now, you've got less room for diversity when using Shuckle.
There's more to cover, but these Pokemon stuck out more than the others to me.
I don't see why we have to makes these long posts about Pokemon that are widely known, especially among good players, to be bad/unviable. I'm seriously stating the obvious here. Any way we can give control of this thread to Gary? :)