Because sylveon is a highly centralizing mon that teams have to bring checks for, you can readily expect to see the same checks 99% of the time. Almost every high-ladder balance / offense team I've seen is running some combination of Entei / Nidoqueen / M-Agg / Empoleon / Metagross / Arcanine / Rotom-Heat as a desperate attempt to stop offensive Sylveon from literally just clicking HV and killing shit.
Offense and even balance to an extent can afford to use Pokemon like Entei and Nidoqueen as checks to Sylveon because they probably will never have to switch into Hyper Voice more than once. Sylveon's typing and bulk are good for an offensive mon, but that doesn't prevent it from getting worn down by hazards and chip damage from the attackers that it can come in on - even defensive Pokemon that it switches in on wear it down in the long run (Chesnaught: Leech Seed or Spikes to limit future switchins; Sableye: puts Sylveon on a HEAVY timer or outright cripples it; etc). There's nothing wrong with having to switch your Entei into Sylveon once as long as you aren't locking a Scarf Hydreigon into Draco Meteor multiple times in the early game. On more defensively oriented/stall teams, Blissey/Aggron/SpDef Empoleon/Arcanine/Bronzong are fine, obviously Sylveon will pressure these archetypes more than others, but it's still not unmanageable and certainly not enough to push Sylveon all the way up to S.
The pressure difference is immense - let's take Entei as an example. Entei is 2HKOd by Sylveon's Hyper Voice after Rocks, so it can switch in and threaten to OHKO with sacred fire. However, sacred fire is not a 0-risk nuke like Hyper Voice. If the Sylveon user is running something like Chandelure or Doom or Arcanine, the entei is then forced to make a prediction. If it makes the wrong choice, it either risks losing the momentum and giving a flash fire boost or losing the entei and doing ~50% damage with Stone Edge or ESpeed.
Switching Chandelure and Houndoom and even Arcanine into Entei is a LOT riskier than switching Empoleon or whatever into Sylveon. I would say that Entei is definitely the more "viable" wallbreaker because Sacred Fire is so good in forcing damage onto Entei's and Entei's teammates' checks and counters, much better Speed meaning it performs a lot better against anything offensive, and even additional "defensive" utility in Extremespeed.
I'm just trying to show that, unlike other nukes, Sylveon's counters are not hard counters even if they predict correctly, and they must also continue to predict correctly once they switch in in order for their countering to be successful.
You can't consider viability in a vacuum of you predicting every switchin and move correctly, you have to look at things on a macro level in which you can be punished for clicking the wrong move. Sylveon really can't be punished for clicking the wrong move that much. Worst case scenario, it does 30-40% to a "counter" and forces it to heal up the next turn or risk getting 2HKOd the next time it tries to switch in.
Again, you're forgetting that Sylveon is also getting worn down while it's Hyper Voicing its counters. It's not like Sylveon can come in over and over risk free and keep taking chunks out of the Steel type until it faints; every time it switches in it's taking damage from the stuff I mentioned earlier. For the last part, that's literally how a Pokemon counters any other Pokemon, i.e. that's the same way Cresselia counters Nidoqueen or Slowking counters Entei.
Another great option for Sylveon is to run Scarf Sylveon in conjunction with NP-Pass Celebi. When you're outspeeding everything below 113+ Spe, there's very little that can take it, and even littler that can take it and kill you and return. On top of being a huge nuke with momentum in b pass, Sylveon also has huge bulk and can take many of the hits from the things that can "deal" with it.
I'll just state the obvious, even +2 Scarf Sylveon isn't breaking through its usual offensive checks, eg Entei Nidoqueen Metagross and all those live a hit after rocks a kill it in return. Not to mention that aside from Hydreigon and a few other minor ones, all the Pokemon that threaten Celebi also threaten Sylveon, so you're gonna have a tough time BPing into Sylveon from Steel-types, Fire-types, Mega Aero/Crobat, etc. Sure you might pick up a surprise kill but now you're running a Sylveon set that requires so much more support than any other set.
All that being said, I do agree that Sylveon /overall/ is deserving of a higher rank than Florges, so I wouldn't be opposed to moving Florges to the bottom of A or the top of A-.
also Mamoswine to S Rank
unless you completely fuck up mamoswine is just ridiculously good. it's a SR setter with insane offensive presence and its offensive and defensive typing allows it to stay relevant throughout the match by blocking volt switches and also preventing S-tier threats like Salamence from setting up due to Ice Shard. it also threatens S-tier threat Tornadus ;)
on the real tho this thing is restrictive in team building and wrecks shit independently of any other mon and yeah
Mamoswine isn't a great Stealth Rock user since it has a very hard time setting up SR and doing the breaking that it should be doing. Sacri's post summed the rest up nicely. It has basically zero defensive utility outside of checking things with Ice Shard, and there's a fair amount of Pokemon that can eat up a few hits and force it out (stuff like defensive Swampert and Forry). I don't see how it's restrictive to teambuilding at all, actually the fact that Salamence is still unquestionably an S-tier Pokemon despite Mamoswine being so good should prove that it doesn't stop anything from being viable and therefore is not restrictive.
Now that that's over with:
Changes:
Mega Ampharos: B to B-
Tentacruel: B+ to A-
Metagross: B to B+. Wasn't a whole lot of discussion on this but Metagross has emerged as a great offensive SR user with the ability to check a lot of key threats
Nominations:
Mega Sharpedo: A to A-. Definitely not as effective or reliable a cleaner as it seemed to be a few months ago, still really threatening late-game to offense but maybe not consistent enough to stay in A (also 2 more checks)
Florges: A to A-
Cresselia: A- to A. Huge threat to offense with its CM set, capable of switching into and beating both NP Celebi and Sylveon with the right investment (max HP, 230 Speed for Crawdaunt, a little bit of Sdef investment with the rest in Def) and a solid answer to Conkeldurr as well. Overall an extremely solid sweeper capable of countering some of the biggest threats in the tier, which it always has been, but it's definitely more comfortable in the bulky offensive environment that UU's currently in.
Other:
Leaving Tornadus where it is, I feel that it fits perfectly near the top of B+. Very threatening once it's on the field, and great utility as always, but not "splashable" to make it up to A- if you consider the other mons in that rank. Also, its unreliability does have to be taken into account here.
Leaving Lucario in B+ as well, although I did move it up to the top of B+ because I think it's pretty close to Infernape, but I think Lucario's checks for either set are common enough to prevent it from rising.
Leaving Escavalier and Shaymin where they are[/quote]