Chandelure is absolutely ridiculous in my opinion. Him + *insert sweeper* is probably the most broken combo ever. I'll just list the number of Pokemon that this thing eliminates or weakens to the point of unusable: Skarmory, Ferrothorn, Scizor, Jellicent, Reuniclus, Latias, Slowbro, Forretress, Tangrowth, Breloom, Dusclops, Serperior, Virizion, Lucario, Heracross, Jirachi, Celebi, Magnezone, Metagross, Sableye, Mew, Genesect, Amoonguss, Dragonite, defensive Salamence, Venusaur, Gliscor, Hippowdon and if you're running Sub/CM, the blobs just become fodder. If you really want to, you can even trap and kill bulky Politoed (which you know, is supposed to COUNTER Chandelure) if you run Sunnybeamer. Like I said in my RMT, holy shit, this is like half the tier. If one Pokemon can trap and rape about half the metagame, you know something is wrong. Most of these Pokemon all form a defensive barrier against something in the tier, and with Chandelure trapping and removing them as easily as just switching in and clicking one of its four moves, you'd wonder how the fuck you can defend against so many threats, especially when we have other broken shit like Manaphy, Blaziken and Excadrill running around.
The main arguments I have seen against banning it are 1) Shed Shell, 2) it's underwhelming because everyone prepares for it and therefore if you play smartly, it doesn't do much. I'll address the first point first. Do you every one of those Pokemon listed above to run a fucking Shed Shell? Sure, stuff like Skarmory and the blobs may be able to get away using it because they have reliable recovery, but do you expect all of them to be able to not run Leftovers and still be effective. Also, some those aren't even walls. Would you get them to not run a Life Orb or whatever offensive item suits them best just because Chandelure exists? Running Shed Shell Dragonite sounds like a brilliant idea, doesn't it? Even if you are a wall and have reliable recovery, it still heavily impedes on your ability to wall when you're forced to carry Shed Shell, firstly you lose out on the recovery, and more importantly, that 6.25% may just push you into an OHKO or 2HKO range. For example, standard Skarmory takes 43.11% - 50.60% from +0 Adamant LO Lucario's Close Combat. With Leftovers, you have a >50% chance to survive being 2HKOed, while without it, you're almost guaranteed to be 2HKOed. I'll try and find more of these, but there are plenty of cases out there.
To the second point, all I can say that that is biggest load of crap and you all know it. That argument applies to every Pokemon that exists and therefore has no validity. You can easily prepare for ExtremeKiller Arceus and it would be quite manageable. In fact, Chandelure is probably even more broken because you can't even switch out against it, meaning it takes the match completely out of your hands. Are you really going to double switch every move in the game just so Chandelure doesn't come in and hand your ass to you on a plate? That's pretty much all I've seen these days. Even then, you can probably kill something and Chandelure immediately comes in and goes "goodbye". Here's just a common example: Your opponent just switched in their Excadrill and used SD. You switch in your Breloom as he SDs. Do you go "oh shit, my opponent has a Chandelure, I can't just Mach Punch this Excadrill right now, I'm going to die to Chandelure if I do, but if I don't use Mach Punch, Excadrill could just kill Breloom right now, and I'll just lose the match right there." Do you want to face this kind of bullshit prediction every fucking match? You can pull the Shed Shell argument again, but I've already covered that. You also have stuff like having Mamoswine out against a 50% Venusaur in the sun. Do you go for the Ice Shard and then get raped by Chandelure, or try and predict the Chandelure switch-in and then just getting killed by Vensaur, and then losing the game because of it? Or do you be ridiculous and run Shed Shell Mamoswine? See what I mean? Even if you do play at the top of your game, it can STILL come in and trap one of your Pokemon and therefore completely make you fall apart. You need to be predicting at 100% if you want to avoid getting dicked by Chandelure, because even if you have like a 90% prediction rate, you'd be sure that that 10% is Chandelure coming in a biting you in the ass.
tl;dr - Get Chandelure out please