Just popping in to nom some mons for a lower rank than they were originally nommed.
Mega Blastoise: someone nommed for B, but it should be C+. Mega Blastoise is cool, but there are a lot of problems with it. Biggest problem is that it takes up your mega slot, which means when you could be using Mega Venusaur defensively or Mega Charizard/Pinsir (who ironically would be fantastic with Mega Blastoise), you're instead using your mega slot for hazard removal/a bulky attacker. Yeah, Mega Blastoise hits hard, and it beats on pretty much every spinblocker. But it's also not as bulky as you'd like it to be when running max HP/SpA and not as strong as you'd like it to be when you run max HP/Def. It's definitely not a bad mon, but it's definitely not B worthy.
Leavanny: someone nommed for C, should be D. It's a cool Sticky Web user, especially because of all the tools it has at its disposal. Grass STAB, Knock Off, Magic Coat, Swords Dance, Agility I think?, Baton Pass. All cools moves that set it apart from Galvantula. But its lower Speed and weaker attacks make Galvantula a generally better choice.
Espeon: nommed for B, should be C. Espeon is disgustingly predictable. Landog U-turns on it, Galvantula's got Bug Buzz, Heatran spams attacks because Espeon can't do shit back, Excadrill's Mold Breaker lets it set up Stealth Rock anyways, Deoxys-S and -D just hang out until Espeon can be killed, Ttar laughs at it, etc. For hazard bouncing, you're better off just running hazard removal. It's not like it's in short supply these days. But its niches as a dual screener and BP recipient are good enough to keep it in C, and Magic Bounce is still a good ability, even if Espeon is trash at making use of it.
Entei: nommed for like A/B+/B or some shit, should be C+/C. Sacred Fire is cool, Extreme Speed is cool, but that's all it has to justify a teamslot and other stuff can run Extreme Speed well anyways. So it's pretty much Sacred Fire that gives it a niche in OU, which is alright, but definitely not A worthy and not really B worthy either to me.
Krookodile: nommed for B, should be C+. I know Fuzznip has an enormous boner for Krook, but B is far too generous for it. Over Landog, it's got the ability to check Aegislash and Tyranitar, STAB Knock Off, and Taunt. But Landog can check pretty much every Fighting-type in the tier, has U-turn which is huge, still has Knock Off even if it doesn't get STAB on it, has the Special Attack to use HP Ice, and has the offenses to run SD/RP. Krook is a cool mon, but its niches are more C+ to me than B.
Other stuff that should probably move but haven't been mentioned:
Mega Medicham: why the fuck is this in A-rank? It's a good Pokemon, yeah, but it's also frail and not hard to outspeed, competing with other faster megas with way stronger STABs and/or setup moves and/or significantly better priority than shitty non-STAB Bullet Punch, hard-walled by Aegislash which is one of the top Pokemon in the meta (like no one is letting their Aegislash die while you have a Mega Medicham around lol). Its Speed is actually not good for an offensive Pokemon. Scarf Genesect outspeeds and does like 50% with U-turn. Mega Lucario outspeeds and either does ~75% with Close Combat or nearly OHKOs with Flash Cannon. Talonflame bones it. Thundurus-I can T-wave or just smack it with a Tbolt. Lati@s bone it. Mega Pinsir demolishes it. Lando bones it. Greninja has a chance to OHKO with Hydro Pump. Gengar destroys it. Keldeo destroys it. Azumarill can't outspeed but can deal a ton with CB AJet or just tank a hit and Play Rough. Charizards only need to win the Speed tie, and Char Y can even live a hit from full. Like it's really not that hard to deal with Mega Medicham because it's slow and pretty much just outclassed by Mega Lucario as a wallbreaker/sweeper anyways.
Mega Absol: should probably drop to C+/C. It's not bad, but why would I use it over any other Mega?
Infernape: C, nothing else really to say here
Tentacruel: C, why would I use it over any other Spinner/Defog user? Its typing is good, but it has so much competition and no permanent rain that it doesn't belong in B.
Jellicent: C+, good typing, Recover, but what does it actually wall anymore?
[edit] on the Chansey shit, it only ever runs Aromatherapy/Heal Bell if it's running Soft-Boiled. Otherwise, it runs Wish/Protect/Seismic Toss/Toxic. Chansey is also only viable on stall anyways, so being "setup fodder" for those Pokemon isn't the end of the world because you will have things to handle those Pokemon as well. Chansey does what it does well, and there's no reason to drop it down when either it or Blissey is going to be on every stall team.