A great amount of Dragalge's also have enough speed to outspeed base 50s like Muk, so it gets 2hked.
Anyways, I finished laddering, so I'll throw my two cents.
I have seen an huge amount of Assault Vest users, don't know if it's a RU thing or simply overpreparing against said three threats but still.
I also think it was a bit rushed up suspecting three 'mons at once seeing we didn't get a chance to analyze the three of them alone with what they brought to the Metagame and whatnot, then again you might say the three of them are a bit "unreal" by RU Standard, so the Council just wanted to do away with those quicky.
The Suspect is about to end though, so it doesn't really matter anymore.
Dragalge: Ban
Honestly, the first time I met Dragalge it was when he ohkoed my steel type of choice at the time, Durant with... Dragon Pulse, while yes Durant has pathetic hp and special defense I was surprised by that, even bulkyer things like Cobalion gets 2hked by Dragon Pulse, this is even excluding Draco Meteor who is able to threaten just about everyone bar fairies who get smashed by Sludge Bomb anyways, the problem doesn't end here, Dragalge is very bulky 65/90/123 are nothing to spit at, coupled by Dragon and Poison who grants important resistances to fire, grass, water, electric and fight attacks, also a neutrality to fairy type attacks, something that no other dragons in the tier can have, as a matter of fact Dragon Pulse from Mega Sceptile fails to ohko
him and with sr on the field only has a low 19% chance to ohko it, the physical defense isn't as great as the special, but its still enough to resists important attacks like Escavalier's Drill Run while HP Fire has a 72% chance to 2hko it without Stealth Rocks AND without items on Dragalge.
Of course Choice Specs Dragalge is by far the most used item at the moment, but one shouldn't leave aside stuff like life orb, draco plate and... assault vest.
Even with Choice Specs, you can't literally stop easily Dragalge, nor actually truly punish him due to its bulk, and this is not even taking hp fire in consideration.
252+ SpA Choice Specs Adaptability Dragalge Draco Meteor vs. 174 HP / 0 SpD Assault Vest Escavalier: 122-144 (37.6 - 44.4%)
252+ Atk Escavalier Pursuit vs. 252 HP / 0 Def Dragalge: 108-128 (32.3 - 38.3%) (on a switch)
You don't really punish Dragalge with Escavalier, pursuit is only a 3hko, even with stealth rocks, Dragalge still has the upperhand against Esca being faster and able to cause more damage, without getting punished too much by switching out.
Special Defensive Bronzong is in the same boat, actually he can't even pursuit Dragalge and earthquake might fail the 2hko, while drill run at least it's a clean 2hko
You could argue that Escavalier/Bronzong might be paired with a wish user like Alomomola but Alo itself is a free opportunity for Dragalge to come in except for scald lucky burn(speaking of it, Dragalge also learns it, and it's useful to cripple incoming Bronzong/Escavalier switch ins), and you force yourself on a risky situation (if Dragalge is specs, otherwise you still lose).
Oh, another fun thing, draco meteor is a clean 2hko with rocks against assault vest slowking, which is also slower than Dragalge.
Cresselia might be an okay "answer" to it, but still, psyshock fails to ohko, and sludge bomb has an high chance to 2hko it (coupled with an additional 30% poison chance, yep).
And yeah, you can't add Cresselia on every team, can you now?
Long story short, you are forced to sack something every time you face Dragalge, this might not be crucial for offensive-minded teams, but defensive and balanced teams greatly suffer from it, well, I suppose it's fun to press a button and watch things easily die, but at some point we need to get serious in order to create competitive tiers.
Serperior: Ban
This guy is probably the only reason I put Protect on Pidgeot, this and... specs jolteon I guess?
In a way its even worse than Dragalge, hes faster than majority of the tier, with only Fletch, Pidgeot AFTER Mega Evolving, Scarf Moltres Hitmonlee if he manages to use Unburden and scarf Emboar.
Ok, really the point is: Serperior manages to easily set up on pokemon like Rhypherior, Alomomola, Kabutops, Gligar if it lacks toxic/Serp has sub etc, and it's not like you can't use these 'mons, they have a valuable, very important role in the metagame, so sooner or later you're bound to create easy set up opportunities for Serperior.
I have seen majority of Serperior holding a Life Orb, but the most scary were the leftovers one, since left gives Serperior artificial bulk, hp rock was also a great choice allowing it to smack non scarf Moltres pdef Golbat (since y'know, hoping to check Pangoro and stuff) Fletch while still able to damage Mega Abomasnow, Mega Pidgeot before mega evolution and Mega Glalie.
Knock Off while situational is a great help against Bronzong, Escavalier and Golbat (especially if the special defensive one) still needs a mention, along with Leech Seed, which, like leftovers makes him more "durable".
Bouffalant might be able to stop him, but yeah its pretty limited as a 'mon, its more a niche thing, Amoonguss has an easier time, though orb +2 hp fire hurts him and sludge bomb fails to ohko him but eh, it's not something that can be fitted on every teams, as such, most of the time you just use something faster that can revenge kill it easily like scarf Moltres, scarf Emboar and Mega Pidgeot, which is cool and all, until you get hit by Glare/Knock Off.
Mega Pidgeot: Leaning towards Ban
Well, it's the suspect I used the most so I might be a little biased here but I can't see him on the same level of Dragalge and Serp, still I think I would pretty much just ban it too, Hurricane confuse chance, coupled by its destructive power is nothing to joke at, most teams I have seen gets smashed by HP Grass variants, thankfully I didn't saw many of them on the ladder, but it's a clean 2hko on Rhypherior, its most used check, while also being faster than the entire non scarf tier with Mega Scep and Jolteon being the only one faster, one of these lose the 1 on 1 against Pid.
Also access to U-turn in order to get in Dugtrio is very dangerous and quite easy to pull off tbh.
