Stall is far too good in the metagame right now, and something needs to be done. So here's a really long post so that I look smart:
The current metagame is essentially composed of teams that are stall, teams that are centered around beating stall, and teams that get 6-0'd by stall. If you've faced any somewhat competent using a stall team, you'll know that these teams are basically impossible to break right now. This isn't just one of those typical "stall is too good pls nerf" complaints; unless you dedicate your team to stallbreaking or use stall yourself, you will lose to stall.
Fluffy: Let's first look at the structure of stall: nearly all stall teams have a chansey as a special wall, and due to chansey's ridiculous bulk, a stall builder only has to consider a small handful of special attackers that chansey does not wall, most of which can be covered within one pokemon, which gets even easier when you consider that chansey gets unaware in AAA and that regenvesters have almost no drawback. The rest of the stall team tends to be centered around physical walls and general utility pokemon, and this part is usually also the weaker part. More often than not, this section of the team will contain poison heal pokemon, magic bouncers, defoggers, phasers, and status users, which can be pretty difficult to fit into 4 pokemon. At the same time, these 4 pokemon also usually ensure that the other two special walls don't fall prey to hazards or status, strengthening the team on the special side as well. Needless to say, it's basically impossible to build a perfect stall team with that formula, and nearly impossible to even approximate perfection.
As for teams of other playstyles, they need to have some formula to beat stall, or else they usually end up losing pretty badly. Most of the time, due to the aforementioned strength of stall from the special side, these teams utilize physical attackers and gradually whittle the team down, because the team by then is nearly impossible to break from the special side.
Now meet fluffy - an ability that basically doubles defense from the physical side (except from certain attacks*). Fluffy turns some of the strongest pokemon in AAA, such as dragonite and lucario, into absolute jokes, as pokemon such as mandibuzz take absolutely nothing from boosted attacks. This results in one pokemon being able to take on a majority of the physical metagame, as there simply is not as much need for multiple layers of physical walls like before. If you need calcs for the sake of satisfaction, calc any physical attacker against any fluffy wall of your choice and you'll see how ridiculous this ability is.
Most of you can see where I'm going with this: fluffy is essentially another "chansey" for the physical side; rather than forcing multiple pokemon to patch up the physical side of stall, you can just slap on a very bulky fluffy physical wall, and account for its weaknesses within another pokemon. This leaves you two extra slots to do whatever you want, and this added versatility is another part of what makes stall so devastating. Before fluffy, stall had trouble making room for a magic bouncer or a dugtrio, but now, adding at least one of these is cost-free and only beneficial and can patch up any holes that the physical and special core left open.
And even on balance or bulky offense teams, fluffy is a pretty much no-drawback option that can completely swing the momentum. It nearly turns all offensive momentum upside down, as most physical attackers become near useless, and fluffy users, unlike chansey, typically carry phasing, switching moves, or attacks that can actually be threatening (like foul play or knock off). Meanwhile, these pokemon can give free switchins to their threats which can obliterate offense due to the presence of multiple other unbalanced abilities in the metagame.
If I'm not playing with stall, why should I add a hoopa or any wallbreaker if I know it's going to get trapped by weavile or dugtrio? Why should I run non-mold breaker rocks+spikes as a way to beat stall if I know that basically all stall can afford to run magic bounce now? Is it really a good idea to add Kartana or Lucario or any physical attacker that I feel like using if I know I'm going to lose all momentum against balance and stall teams with fluffy? Fluffy pushes stall way over the top, and it needs to see a ban if the metagame needs to become any healthier. Evidence of this includes the fact that 4 out of the top 5 ladder players use stall, and trying to prepare for and win against stall teams in the current metagame is near impossible.
*Some people have been arguing that there are ways around fluffy. Yes. There are ways around fluffy. Some viable ways around it from pure physical attackers are fire punch, v-create, sacred fire, stone edge, earthquake, seed bomb, and icicle crash. Yes, you can use these moves. But no, this doesn't change just how much fluffy compresses stall teambuilding. It's much, much, easier to cover the primary users of these moves (victini, weavile, entei, mamoswine, terrakion, garchomp, kyurem-b, hoopa) within a couple pokemon (for ex. dugtrio and tapu fini covers almost all) than covering all physical attackers within just 1 more pokemon, and the team with fluffy will almost always have much more useful utility pokemon than the team without. The end result is a stall that ends up being nigh unbreakable from the physical side, nigh unbreakable from the special side, and immune to any non-standard stallbreaker that can get out of hand. If you're saying fluffy isn't broken because intimidate basically does the same thing and wasn't broken, that's like saying 6th gen parental bond wasn't broken [on physical attackers] because huge power was stronger. If you're saying fluffy's not as broken as fur coat so we shouldn't ban it, well, I don't think rayquaza would be as broken as mega rayquaza in OU, but that doesn't mean we should free rayquaza. Whatever the case, fluffy makes stall (and even balance) too strong and eliminates far too much of the metagame, and it needs to be banned.
tl;dr fluffy's broken just read it lol it doesnt take that long if u sincerely care about competitive almost any ability
some other needed future suspects: Poison Heal, Protean, Hoopa-U, Stakeout/Illusion, Dragonite, Kyurem-B - someone else can write these up
Poison Heal: similar to "the fluffy effect", but made even worse given the emergence of 1k arrows zygarde, and it's still good on everything else. Draw-free, extremely potent, and breaks a ton of pokemon, esp. Suicune/Snorlax/Zygarde
Protean: too much power.
Hoopa-U: see above
Stakeout/Illusion: Don't see this suspect happening soon, but give it time and it will need to happen. The ability to just get rid of counters for free and/or force your opponent to sac counters to other pokemon is too good.
Dragonite: espeed game too strong, versatility game too strong, too much power
Kyurem-B: too much power
