To be quite blunt, Raikou's choice scarf set is bad. Really bad.
252 SpA Raikou Extrasensory vs. 4 HP / 0 SpD Heracross: 168-198 (55.6 - 65.5%) -- guaranteed 2HKO
252+ SpA Raikou Aura Sphere vs. 0 HP / 4 SpD Hydreigon: 192-226 (59 - 69.5%) -- guaranteed 2HKO
252 SpA Raikou Thunderbolt vs. 0 HP / 4 SpD Darmanitan: 217-256 (61.8 - 72.9%) -- guaranteed 2HKO
252 SpA Raikou Thunderbolt vs. -1 0 HP / 4 SpD Victini: 202-238 (59.2 - 69.7%) -- guaranteed 2HKO
252+ SpA Raikou Aura Sphere vs. 4 HP / 0 SpD Krookodile: 236-278 (71 - 83.7%) -- guaranteed 2HKO
I've just selected quite a number of common choice scarf mons that one may want to use Raikou to outspeed, and the damning fact is without significant prior damage, Raikou doesn't get the revenge kill. IDK about other people's opinions, but to me that is really bad if I want to stop a sweep from moxiecross, moxiedile, hell even darmanitan unless it takes a fair chunk of SR + FB recoil. Being unable to KO victini after a stat drop from V-create really stinks too. Really Raikou is subpar for using a scarf.
SubCM is dead. Sashzam, blissey and goodra, alongside the other viable ground types and snorlax just make it a waste of team slot to use.
Really the only thing it has left is LO/Specs, of which I'm not certain enough that it warrants something good for a rating. I reckon bar the scarf comments, kitten milk has got it right.
You didn't even bother mentioning the following: if raikou does want to run aura sphere, which allows it to do some amount of damage to special walls like Snorlax or Umbreon, it must run a rash nature, both compromising its special bulk as well as allowing other scarfers, like Ape or Mienshao, to easily outspeed and take it out; I fully agree on
Raikou --> B-
Hmm...
Raikou (A-) -> B- | This may seem like an extreme drop, but Kitten Milk and silenced before me have perfectly explained exactly why Thundercat has fallen from grace. The June drops are
extremely harsh to it; Blissey and Goodra wall the everloving fuck out of Raikou, Snorlax can still deal with it quite well, Alakazam quickly disposes of most Raikou variants, as Psyshock hits Raikou's average 75 Defense. As illustrated by silenced, Raikou is a really shitty Scarfer, as it just can't KO what it needs to KO. Mega Ampharos has an overall far better typing with additional resistances, as well as a secondary Dragon-type STAB and it can perform as both a defensive pivot
and a setup attacker, even using Raikou as setup bait. There's really little reason to consider Raikou in current UU; its power is lacking, it's got severe coverage issues and is overall outclassed, so at that I say
Raikou for B-.
Mega Aerodactyl (A+) -> S | On another note, I've been thinking a bit about this rise and will explain. Mega Aerodactyl is an incredibly versatile and powerful threat in XY UU, hands down the best Mega Evolution in the tier. It's able to check an absurdly large amount of Pokémon in the tier and provides a solid answer to Fire- and Fighting-types that run rampant in UU, such as Infernape, Victini, Darmanitan, Mega Houndoom, Mienshao and Heracross. Mega Aerodactyl possesses a great 135 Attack stat which, coupled with its mostly Tough Claws-boosted coverage movepool and STAB Aerial Ace, allows it to put a serious dent into everything; due to its wide coverage, Mega Aerodactyl can hit a large myriad of Pokémon supereffectively. Its blazingly fast 150 Speed makes it so that the prehistoric beast can use an Adamant nature for maximum power while still outspeeding most prominent threats. Mega Aerodactyl's bulk isn't half bad for a sweeper, either, sporting 80/85/95 defensive stats. Due to its useful resistances to Bug and Fire, Mega Aerodactyl can run a specially defensive Defog set with SR that not only pressurizes the opponent's hazard setters, but allows the beast to set up hazards to support its own team with as well.
Unfortunately, Mega Aerodactyl has some flaws in the form of a weakness to SR, limiting its switch-in opportunities and Defogging potential. Its nasty Water-type weakness plagues it, too, considering the large amount of Water-types in the tier; fortunately, Mega Aerodactyl can run Crunch to get past Slowbro.
Countermeasuring the few flaws Mega Aerodactyl has are many positive points that make this Pokémon shine in the UU tier as one of its greatest threats.
Mega Aerodactyl for S.
Again, I fully agree on Raikou.
On the Mega-Aero opinion, however, I have my doubts.
Its blazingly fast 150 Speed makes it so that the prehistoric beast can use an Adamant nature for maximum power while still outspeeding most prominent threats.
The only problem I have with this is the Mega-Evolving turn. While it isn't particularly bad off, still outspeeding +natured base 115s, it still loses out to some threats, namely alakazam, and some slower scarfers after it Mega-Evos. Probably not that big an issue.
Mega Aerodactyl can run a specially defensive Defog set with SR that not only pressurizes the opponent's hazard setters, but allows the beast to set up hazards to support its own team with as well.
This seems like a stretch. To be honest, I fail to see any fire type that is particularly dissuaded by mega-aerodactyl; Darm OHKOs with rock slide, Victini can sometimes OHKO with bolt strike if scarfed, Arcanine does decent damage with Wild Charge, or simply Will-O-Wisps to cripple, making Aero set up fodder, and Chandelure, if scarfed, can 2HKO mega Aero anyway and doesn't care. Rotom-H can burn on the switch or volt switch out, giving it momentum; finally, having been a major proponent of Support Mega-Scizor in early OU, I can attest that defensive pokemon generally don't like being megas; having to mega evolve to achieve decent bulk, as aero does, limits its usefulness before it is able to switch into anything and start getting off defogs, and by the time it does switch in, it will generally have suffered rock damage already. Additionally, this support set has trouble clearing hazards against quite a few users; Forretress and Bronzong, for instance, do quite a number with their STAB gyro balls. Swampert runs scald, which chances the burn, again making aero set up fodder, and the nidos can either hit with supereffective ice beam or thunderbolt, while also being able to do quite a bit of damage with Earth Power on a predicted roost. Jirachi can paralyze or just Iron Head on the switch. Mew can Wisp, and Aggron-Mega's going to laugh from any uninvested physical hit, and OHKO back. Assuming Aero runs Defog, Stealth Rock, and Roost, he only has one attack for coverage; the most common option, Stone Edge, fails to damage any of these hazard setters in notable ways. Metagross, of course, can OHKO easily with Meteor Mash, while no attack can OHKO back. While I haven't calced it, I feel fairly confident that Galvantula can at least 2HKO with thunder, forcing Mega-Aero to go for a roost its first turn after coming in, and risking a 30% of paralysis- twice. Frankly, Mega-Aero is better off running its standard offensive set in almost any situation.
Honestly I see this as a set to specifically counter one pokemon- roserade- and very little else. Any only after the sleep clause has been activated.
Mega Aerodactyl can run Crunch to get past Slowbro.
All right, after scouring your post, you really didn't mention Mega-Aero's biggest flaw; this is the closest you've come.
Mega-Aero, frankly, doesn't like defensive teams. He can't do a whole lot against dedicated stall. Mons like Quagsire, Swampert, Duoblade, Cobalion, and Hippowdon might not be able to consistently switch into Mega-Aero by themselves throughout the match, getting worn down over time (although some, like phys defensive Hippo, can do it fairly well); however, when M-Aero is facing more than one physical wall on a team, it's forced to rely on prediction to impact the match in any way- and generally, you don't want to have to rely on prediction, especially if you're trying to ladder into the higher tiers; reliance on prediction is usually a sign that you've lost control of the match; I shouldn't need to explain why being forced into prediction wars to win is not a good thing.
For this reason, Mega-Aero has a tough time fitting into all team archetypes.
One additional flaw is that Mega-Aero is possibly the most status weak Pokemon in all of UU (okay, maybe that's a stretch, but the point stands)- Aero is literally crippled by every status in the tier; Burn, Paralysis, and Sleep all incapitate him (and toxic, but to a lesser extent; no more than other offensive mons), forcing him to also need the support of a cleric and/or status absorber.
All in all, Aerodactyl-Mega is a quite good pokemon, capable of making a huge difference against many teams, yet it still does require certain amounts of team support which simply aren't offset by its boons.
Mega Aerodactyl should stay A+ rank.